• The Evolution of State/Provincial GWS Governance

After agreeing on the 1956 Great Lakes Compact, GLB states/provinces adopted bulk water use and diversion counsels of successive binational agreements. In so doing, they followed the historical trend of overlooking sustainable aquifer yield requirements

and favoring surface water preservation objectives. As such, the focus of this assessment is on the governance of smaller volumes of GLB groundwater use within the study period. This is because, despite much of the theoretical foundation and rudimentary groundwater quantification and modelling methodologies being established by 1940 [62], there has been considerable variation in the degree to which these policies and decision-making standards kept pace with these scientific advances and took sustainable yield considerations into account [69]. We also evaluate court rulings to resolve groundwater use conflicts during the study period. As the only state wholly within the Basin's boundaries, we focus analysis on Michigan's court decisions as its many landmark rulings demonstrate well how groundwater conflict resolution has been historically treated in case law.

#### I. Ontario

Ontario had some of the earliest policies in place impacting GWS in the study period. Its Ontario Water Resources Act (OWRA) mandated licensing and pumping rate data collection since 1961 [67]. A 1990 OWRA amendment introduced more stringent requirements for bulk water use than those of the 1985 Charter, requiring permits for taking over 50,000 L per day, environmental impact assessments (EIAs), and a graduated approach to PTTW fees. Reflecting consideration of lower quantities and replenishment rates of GWS, fees ranged from none for taking water from low-environmental-impact sources, to USD 3000 for groundwater PTTWs issued in high-use regions and/or for water-bottling purposes (Section 34). The 2001 Ontario Municipal Act was the only GLB policy within the study period mandating inclusion of municipalities in PTTW decision making. On regulating pumping from both small- and high-capacity wells, a 2002 Safe Drinking Water Act amendment mandated tracking of pumping rates to avoid uptake of brines, thus reducing aquifer over-pumping risks. The 2002 Ontario Low Water Response Act considered temporal aspects impacting groundwater availability, setting progressive restrictions on water pumping corresponding to reducing levels of streamflow and/or precipitation in times of drought.

#### II. Pennsylvania

Far stricter than most GLB states/provinces, in Pennsylvania there has been longstanding consideration of the cumulative impacts of smaller water takings (even from aquifers underlying private property), temporal limits to groundwater use, and focus on EIAs before granting bulk groundwater permits. The earliest Pennsylvania statute impacting the Basin's GWS was the 1956 Water Well Drillers License Act (32 P.S. §645.1 et seq), which required users to request and renew annual licenses for small- and large-capacity wells and reporting of water table levels. The 1978 Emergency Management Services Code (35 Pa.C.S. §7101 et seq.) was the first GLB policy to mandate reduced groundwater use during droughts. The 1984 Safe Drinking Water Act appeared to consider sustainable aquifer yield by empowering municipalities to issue permits, at an annual fee capped at USD 500 for persons taking groundwater from publicly owned aquifers. It also required EIAs on aquifers as part of groundwater permit requests. Finally, the 2002 Water Resources Planning Act 220 (27 Pa.C.S. Chapter 31) made it compulsory to report groundwater withdrawals for domestic use from aquifers within private land when exceeding 10,000 gallons per day.

#### III. Minnesota

Unlike Pennsylvania and Ontario, Minnesota has had far less consideration of sustainable aquifer yield requirements in its statutes and regulations impacting GWS. Instead, the state has had a tradition of having little to no regulations for the use of groundwater within private land, rather focusing on the protection of water within publicly owned lands. In 1897, Minnesota Law first adopted the term public waters (Minnesota Water Law Section 103). However, groundwater was excluded in the original definition of public waters, instead limiting public waters to large lakes and streams that were capable of beneficial public uses such as water supply, fishing, and boating. All other waters were deemed private and beyond the regulation of the state. The catastrophic drought of the mid-1930s demonstrated the need for more stringent water protections, which for the first

time included groundwater, as the Minnesota Water Law was amended empowering the state to issue permits to protect the public's interest in the amount of water available for use. Permits were required for large-quantity uses of public waters as well as for the appropriation of public waters for agricultural, industrial, and commercial sectors. Yet, the permit fee structure remained the same for groundwater and surface water, thereby disregarding the differences in availability and recharge rates.

In 1976, the Public Waters Inventory Program was introduced to track water levels (Laws of Minnesota 1976, Chapter 83 and Laws of Minnesota 1979, Chapter 199), reiterating the definition of public waters as those serving "beneficial public purpose" and for the first time including aquifer recharge as public waters. A 1979 amendment confirmed the location of public waters as those within lands to which the State of Minnesota or the federal government hold title. It also made it mandatory for all 87 counties of Minnesota, including the ones to the north east within the GLB, to participate in the public waters inventory. The 1990 Allocating and Controlling Waters of the State (Laws of Minnesota 1990. 103G.255) amended several previous laws to provide further clarity on the state's role in conserving sufficient water resources for public use; however, it did not include specific hydrogeological science-based actions for conserving groundwater. Aiding the protection of groundwater within private and public lands, in response to the 1987–1989 drought, in 1990 the Minnesota Department of Natural Resources was mandated to develop a drought plan (Minnesota Statutes Section 103G.293). Still in use today, the resulting Minnesota Statewide Drought Plan consists of a set of prescribed local action responses to five different conditions/phases of climate (normal to extreme drought) [70].

#### IV. Wisconsin

Though Wisconsin has not had a long track record of laws reflecting sustainable aquifer yield considerations, and did not have regulations mandating reduced groundwater use during droughts over the study period, it has more recently developed one of the more comprehensive water use and aquifer protection policies of all GLB states/provinces. Its 1983 Comprehensive Groundwater Protection Act 410 (Chapter 160, Wisconsin Statutes) established the Groundwater Coordinating Council to assist state agencies' coordination of water conservation and provision of GWS scientific data. On smaller-capacity wells, it empowered municipalities to regulate—under Wisconsin Department of Natural Resources (DNR) supervision—construction and pump installation for some private wells. The 2003 Groundwater Protection Act (Wisconsin Act 310) mandated EIAs before granting PTTWs for high-capacity wells. The Act also defined the spatial extent of Groundwater Management Areas, mandated pumping rate reporting, and established a decision-making standard for addressing water quantity issues in rapidly growing areas of the state. However, with annual PTTW fees set at USD 100 for both surface water and groundwater, economic incentives did not appear to consider their relative quantity and recharge disparities [71].

#### V. Indiana

Indiana's approach to GWS governance featured some of the least physical—environmental considerations for protecting GWS of all GLB states/provinces within the study period. Since 1860, Indiana has applied the "Reasonable/Beneficial Use system" to govern both surface water and groundwater uses [72]. Like Minnesota, its application of the Reasonable Use Rule in the Indiana Code (IND. CODE § 14-25-7-6.) permits " . . . the use of water for a beneficial use in such quantity and manner that is (1) necessary for economic and efficient utilization, and (2) is both reasonable and consistent with the public interest." The first statute to provide some GWS protections was the 1985 Emergency Regulation of Ground Water Rights Act (IC 14-25-4). However, the law was concerned with protecting property rights to groundwater as it protected owners of small-capacity wells from the impacts of high-capacity wells if they significantly lower GWS levels within their properties. Still in use today, this law has been further reinforced in Indiana case law that has held landowners liable for all types of damages caused by the excessive removal of groundwater, including subsidence damage. This is illustrated in the 1998 Indiana Court of Appeals ruling against the GLB City of Valparaiso. Damages were awarded to the plaintiff for land subsidence

caused by the City's over-pumping of GLB groundwater (City of Valparaiso vs. Defler, 694 N.E.2d 1177, 1180-82). The Court of Appeals stated that reasonable and beneficial use of groundwater must be maintained to avoid harming the rights of adjacent landowners. The 2003 Water Rights and Resources Act (Indiana Code 14-25-1(1)) furthered this approach to GWS governance. While it defined the types of water subject to government protection for the public welfare, it did not include groundwater. Similar to Minnesota, Indiana provided some recommendations to protect GWS in times of drought. Its 1994 Water Shortage Plan included environmental indicators of water shortages with corresponding groundwater use and management responses.

#### VI. Michigan

Prior to the passage of the 2005 GLSWRA, Michigan's statutes largely omitted standards to control groundwater use that reflected sustainable aquifer yield considerations [73]. In addition, most controls on groundwater use were set by the courts in settling groundwater use disputes, and rulings were primarily concerned with ensuring equitable access rights to groundwater within property limits. The earliest of these rulings was from the Michigan Supreme Court in the 1917 Schenk vs. City of Ann Arbor case (196 Mich 75, 163 NW 109), where it was found that the City of Ann Arbor did not have greater rights to withdraw groundwater for the provision of public water supply than a private landowner did. The court also ruled on another landmark case, Bernard vs. City of St. Louis in 1922 (220 Mich 159, 189 NW2d 891), in favor of the plaintiff, requiring the City of St. Louis to reduce groundwater withdrawals to maintain adequate water for the plaintiff's use, and awarding compensation for pumping equipment that the plaintiff had to install. In 1982, the Michigan Court of Appeals reaffirmed the outcome of Bernard vs. City of St. Louis, ruling in the Maerz vs. U.S. Steel Corporation case (116 Mich App 710).

Statutes that did cover GWS were first established in the late 1970s. Reflecting the Absolute Ownership Rule in stating that municipal governments had no authority to curb groundwater uses within private land, the 1978 Michigan Public Health Code (PA 368, MCL 333.1101 to 333.25211) indicated that "a local unit of government shall not enact or enforce an ordinance that regulates a large-quantity withdrawal." Another was the 1981 Michigan Right to Farm Act (P.A. 93 Sec. 3 (3)) that listed conditions that offered farmers protection from nuisance suits. Noting that it cannot be applied to resolve water use conflicts, the Act precluded installation of new irrigation equipment or new technologies as grounds for groundwater use complaint suits, paving the way for installation of higher-capacity pumps adding pressure on aquifers. Michigan took its first steps towards conserving GWS based on sustainable aquifer yield considerations when it passed the 1994 Natural Resources and Environmental Protection Act 451 (Mich. Comp. Laws § 324.30106), requiring EIAs before granting permits to take groundwater. The 2003 Aquifer Protection and Dispute Resolution Act added further protections by setting withdrawal thresholds based on a regional groundwater model that can assess the degree to which aquifers are overexploited.

On economic policies impacting GWS during the study period, Michigan's court rulings have had implications on the extent to which free trade treaties could be applied to access groundwater prior to the 2020 USMCA. The Michigan Court of Appeals 2005 ruling on the Michigan Citizens for Water Conservation (MCWC) vs. Nestle Waters North America Incorporated (269 Mich. App. 25, 709 N.W.2d 174) is one of the most significant cases. Nestle previously purchased groundwater rights to a Sanctuary Springs property in Mecosta County, within which it established four high-capacity wells that pumped groundwater at a rate of 400 gallons per minute (576,000 gallons per day). The 1994 Natural Resources and Environmental Protection Act 451 was considered by the court in ruling for the MCWC, preventing Nestle from continuing operations. Considering the MCWC as riparian property owners negatively affected by Nestle's wells, the court found that Nestle's withdrawals unreasonably interfered with MCWC's rights. The court also noted the harmful impacts that Nestle's groundwater extraction was having on the ability of wetlands and watercourses to provide ecosystem services, including the reduction of their

ability to provide fisheries habitat, water filtration, and to prevent erosion and flooding. The court ordered Nestle to cease operations pending determination of more sustainable groundwater withdrawal rate, allowing consideration of sustainable aquifer yield factors. It was not until after the study period, in the 2006 amendment to the 1994 Natural Resources and Environmental Protection Act 451, that any statutes were passed that regulated the removal of any quantity of GLB groundwater from an aquifer for free trade purposes [74].

#### VII. New York

Prior to the 2005 GLSWRA, New York statutes impacting GWS had minimal guidance that reflected sustainable aquifer yield considerations [75,76]. The first was the 1972 New York Environmental Conservation Law (Chapter 43-B) that set standards to reduce overpumping to prevent upwelling of brines to maintain water quality. The other significant measure during the study period was the 1988 Great Lakes Water Conservation and Management Act (NYS ECL § 15-1501 et seq.) that imposed EIA requirements on public water suppliers that withdrew large amounts of GLB water.

#### VIII. Illinois

In Illinois, groundwater uses have for the most part proceeded without reasonable use limits, volumetric controls, or policies restricting groundwater use in times of drought. Additionally, Illinois is one of two GLB states initially using the Absolute Ownership Rule in case law applied to resolve groundwater use conflicts, applying it well into the 1980s [77]. The Edwards vs. Haegar (180 III. 99) ruling in 1899 allowed for landowners to use groundwater without concern for impacts on neighboring users until the passage of the 1983 Water Use Act. In this Act, the applicability of the Reasonable Use Rule to govern the State's groundwater withdrawals was confirmed. This was reaffirmed in the Bridgman vs. Sanitary District of Decatur (164 III. App. 3d 287 4th Dist.) ruling, which stated, "By using the terms 'natural wants' and 'artificial wants' in the definition of reasonable use . . . the legislature has adopted the same standards for groundwater withdrawals as that which applies to surface water withdrawals." Another step towards protecting GWS was the adoption of the 1987 Illinois Groundwater Protection Act, which enacted a series of technical programs and procedures to monitor statewide well levels. Though the 1980 Supreme Court Ruling (Wisconsin vs. Illinois, 449 U.S. 48) established the Chicago Diversion, precluding the state from any 2005 GLSWRA obligations, Illinois permitted bulk groundwater pumping for domestic uses following its 1996 Rules and Regulations for the Allocation of Water from Lake Michigan.

#### IX. Ohio

As per court rulings dating from 1861, Ohio initially applied the Absolute Ownership Rule in regulating how much groundwater landowners could use, joining Illinois as the second state to do so in the GLB [78]. Courts provided no legal remedy for complaints of excessive use until a 1984 Ohio Supreme Court decision in Cline vs. American Aggregates Corporation, which adopted the Reasonable Use Rule in its ruling. The court placed a duty on landowners to make sensible use of groundwater to avoid harm to the groundwater rights of nearby landowners. The next significant step to safeguarding GWS was the 2003 amendment to the Groundwater Rules and Regulations (Ohio Administrative Code Reg. 3745-34) which required groundwater use permits to withdraw over 100,000 gallons per day, the same volumetric limit set for surface water.

#### **4. Discussion**

Results of our CPT analysis pinpoint the causes of gaps in the present day GWS governance framework that have led to emerging groundwater supply vulnerabilities in drought-prone and/or groundwater-dependent GLB communities. Referring to key aspects of CPT theory, below we outline the empirical manifestations and causal mechanisms successive governance milestones/amendments and court rulings within the study period that comprise the causal chain linking historical causes to present-day outcomes.

• Causes and Outcomes

The greatest strength of GWS governance over the years has been its facilitation of scientific research and data collection, which if applied, would have been relevant to devising groundwater use policies and decision-making standards based on sustainable aquifer yield. This is evidenced with federal governments' early establishment of the USGS and GSC, and their long-term collaboration with the states/provinces in aquifer mapping and monitoring GWS levels [67,68]. GLB states/provinces have fairly consistently required GWS-level data collection, and in some cases, have long required pumping-rate reporting, such as in Ontario, Pennsylvania, Minnesota, and Wisconsin. At the binational level, the 1956 Great Lakes Basin Compact was a key milestone as it initiated the whole-of-basin approach to GWS governance that has come to characterize successive agreements, catalyzing binational hydrological research and data sharing on GLB water resource use [65].

Data and science on aquifer geophysical parameters, flow rates, as well as technologies and methodologies for quantifying and simulating groundwater flow have been steadily improving over the study period. However, our findings suggest that although governments at multiple levels have facilitated much of this science that is relevant to sustainable aquifer yield, they insufficiently leveraged it to develop groundwater use and conservation rules over the study period. This feature is the root cause of present-day GWS governance weaknesses and groundwater decline outcomes.

CPT points to legal principles originating from 19th century court decisions and scientific understanding of groundwater flow systems as the fundamental cause of these outcomes. The oldest of these is the Absolute Ownership Rule. Court deliberations in its earliest documented application, the 1843 Chasemore vs. Richards ruling (1843-60 All E.R. 77, 81-82 H.L. 1859), shed light on the incipient state of hydrogeological science at the time that supported the creation of the legal concept that groundwater use could not be governed because its quantities and flow directions were "unknowable". From 1776 to 1865, the science of hydrogeology was characterized by slow growth in the understanding of underlying principles, especially in the Great Lakes region where springs were plentiful, not requiring early settlers to develop wells to access groundwater, or consider impacts of overuse [62]. Therefore, when the Reasonable Use Rule was later set to govern groundwater use, it was largely oriented towards protecting the rights of adjacent landowners to access groundwater within their property limits. Additionally, for much of the study period, GWS conservation for the greater public good was not prioritized, given the Public Trust Doctrine's incorporation into early state/provincial constitutions that regarded only surface water as a common, public resource. The Underground Stream Doctrine further entrenched this paradigm, as governments typically only stepped in to protect GWS for the purpose of safeguarding surface water.

It is from this scientific and legal basis that during the study period, successive GLB governments and courts at multiple levels largely failed to devise policies and standards for groundwater use and conservation based on sustainable aquifer yield. Carried through to the present day GWS governance framework, we outline the causal mechanisms culminating in current governance weaknesses and GWS decline outcomes.

• Empirical Manifestations and Causal Mechanisms

Focusing first on policies and decision-making standards controlling groundwater pumping, successive, multilevel statutes generally omitted specific, science-based measures based on sustainable aquifer yield during the study period. Echoing Underground Stream Doctrine paradigms, governments typically interrelated surface water and groundwater rights of use, not containing evidence of appreciation that there is five times more surface water than groundwater stored in the Basin [1]. With most governmental controls for groundwater use limited to bulk quantities, it is noteworthy that since being introduced in the 1985 Charter, the same high volumetric water use thresholds were used to define bulk surface water and groundwater, seeming to be better suited to surface water's greater availability and quicker recharge rates [79].

Another significant governance blind spot was the paucity of regulation of smaller quantities of groundwater uses. This is seen in groundwater exports from the Basin in containers 20 L or less being allowed in successive binational agreements leading to the 2005 GLSWRA; these agreements being purportedly aimed at preserving the quantity of all GLB waters. More evidence is that most GLB states, except for Ontario and Pennsylvania, did not have controls on smaller volumes of groundwater pumped within private land. Reflecting the legal principles of the Absolute Ownership Rule, governance focused rather on standards for well construction and pump installation. Groundwater pumping for firefighting and agriculture, regardless of the quantity, was also unregulated, despite the latter being the largest groundwater consuming sector in the Basin [57,59].

Past court rulings also provide more empirical manifestations that reflect 19th century scientific and legal principles. Rulings resolving groundwater use disputes seem to have been rather focused on ensuring equitable groundwater rights of landowners rather than preserving aquifer storage [80]. Courts have generally ruled in favor of those with the deepest wells and highest-capacity pumps, such as in the Bralts and Leighty (no date) Michigan court ruling that "if a neighbor complains that your irrigation pumping is causing their well to go dry, a prudent response would be to offer to deepen their well and consider it an irrigation expense." In other instances, courts typically enforced the Reasonable Use Rule and/or Underground Stream Doctrine and applied jurisprudence on surface water, given its longer track record of case law, to resolve other groundwater use conflicts [72]. Notable examples are deliberations in the City of Valparaiso vs. Defler (694 N.E.2d 1177, 1180-82) ruling in Indiana and the Bernard vs. City of St. Louis ruling (220 Mich 159, 189 NW2d 891) in Michigan.

On GWS conservation, multilevel policies and decision-making standards had a mixed record on considering sustainable aquifer yield during the study period. Positive developments were the introduction of EIA requirements in PTTW decision-making standards for high-capacity wells beginning in the 1980s in some states/provinces, as well as their protection of waters needed for aquifer recharge. Moreover, with regard to the temporal dimension of safeguarding GWS, states/provinces introduced voluntary, judicious water use policies to protect GWS during droughts, with Pennsylvania and Ontario being the only jurisdictions where this was made mandatory during the study period.

Economic policy tools also reflected 19th century legal and scientific concepts, and typically appeared to disregard sustainable aquifer yield. There is little evidence to suggest that they considered quantitative evaluation of the trade-offs between future and current groundwater withdrawals that would be required for dealing with growing groundwater insecurity [63]. To illustrate, historically, fees for municipal water supply and state/provincial well permits and PTTWs have been low or nonexistent. Moreover, as these fees generally were not differentiated from the pricing structure for surface water, multiple levels of governments did not consider groundwater's relative scarcity and lower recharge rates, providing little economic incentives for reducing groundwater use.

• Causal Linkages

Legal principles originating from 19th century groundwater science do not appear to have persisted in successive court decisions, policies, and decision-making standards due to a lack of competence or understanding of hydrogeological science. Much of the theoretical, engineering, and methodological underpinnings needed to quantify groundwater and simulate its flow directions and rates were established since the 1940s [62], and GLB governments have demonstrated their ability to leverage these scientific advances towards safeguarding groundwater quality. GLB governments at multiple levels have had laws protecting groundwater quality since the 1970s that explicitly considered modern science on geophysical and environmental parameters [17]. Kickstarted with major environmental disasters such as the Love Canal catastrophe that leached hazardous chemicals into underlying groundwater in the Niagara escarpment, to widespread eutrophication of Lake Erie, general awareness of GLB water quality crises shifted public opinion, leading to sweeping policy changes [81]. Since then, consecutive amendments of groundwater quality

regulations have mostly kept pace with innovations in science, with there being some successes in improving groundwater quality across the GLB [82].

The above suggests that path dependency may be the likely rationale for GWS governance and groundwater quality governance having such contrasting outcomes. The phenomenon of governments starting down a particular track, making the costs of reversal or change extremely high to overcome [83], path dependency is the likely causal link through which GWS governance weaknesses were able to persist well into the present-day governance framework, inexorably contributing to growing water insecurity in high-stress locales. Hansen [84] contends that "path dependence is established only when it can be shown that policy change was considered and rejected for reasons that cannot be explained without reference to the structure of costs and incentives created by the original policy choice.". As such, policies are inherently challenging to reform [85], even when suboptimal to address problems [86]. Often, policymakers typically must wait for critical junctures or exceptional opportunities to enact governance reform [87].

In this context, the evidence conveys that successive GLB governments have had little inducements to amend GWS governance as growing groundwater insecurities have been largely localized and location-specific problems [88]. This is compounded by GLB residents generally having low water risk literacy, lulled into the "myth of water abundance", relatively unaware of risks posed by droughts and rising uses [89,90]. With growing groundwater vulnerabilities not yet garnering widespread public attention, or becoming a Basin-scale problem, public pressure or significant inflection points have not yet demanded GWS governance reforms considering sustainable aquifer yield.

#### **5. Conclusions and Recommendations**

Projected increases in climate and human pressures will continue to undermine groundwater security in a "do nothing" policy scenario. Climate change will increase precipitation in the Great Lakes region. However, its pattern will be progressively altered, concentrating more precipitation within winter months when the ground is frozen, and infiltration is reduced. In these conditions, aquifer recharge is expected to decrease by up to 20% [5]. Currently, 10% of the US population and 40% of the Canadian population reside within the GLB [91], with some of the fastest growth in inland peri-urban communities. For many communities, groundwater is often the sole source of public water supply: e.g., almost half of Michigan residents and a third of Ohio residents depend on GLB groundwater for public water supply [92]. With industry increasingly being attracted to the Basin, drawn by clean waters and cheap water prices, these trends have already contributed a thirtyfold increase in regional groundwater withdrawal, currently estimated at 160,000 L/day [2]; as well as an overall 15% increase in groundwater consumption across the Basin, while surface water consumption decreased within the study period [93]. If left unchecked, these trends are likely to proliferate groundwater overuse, particularly in population growth and industrialized hotspots, raising the specter of groundwater insecurity deepening in high-stress locales.

To contend with rising GWS threats, our findings argue strongly in favor of reforms of policies and standards regulating groundwater pumping, use, and conservation. As demonstrated with improvements made with water quality governance due to public pressure, inflection points can make fundamental governance reforms possible [87]. Considering this, our first recommendation is to raise awareness of the true availability and vulnerability of GWS in the Basin. As a water-rich region, these location-specific vulnerabilities are often overlooked. Therefore, raising awareness on the increasing cases and socio-environmental drivers of GWS vulnerabilities across the Basin is key.

Secondly, we urge for groundwater use governance to keep pace with scientific findings of the twenty-first century. It is clear that the Absolute Ownership Rule that underpins the evolution of GWS governance was based on legal concepts predicated on 19th century science, as governments avoided the establishment of specific rules to govern the use of a resource they could not quantify or trace. Through path dependency, they instead

applied rules originally devised and better suited to maintain surface water quantity, despite advances in science that increasingly recognized groundwater as quantifiable resources supporting vital environmental functions and economically valuable human uses. In so doing, GLB governments at multiple levels have not recognized that the original interpretation and establishment of these rules were very much a product of their time.

Since then, a great deal more knowledge and data on groundwater flow rates, directions, and quantities have been accrued as the hydrogeological scientific discipline matured. Twenty-first century innovations such as Big Data, GIS, remote sensing, and machine learning technologies to estimate aquifer geometry, quantify GWS, and model groundwater flow directions [94] carry the promise of faster, cheaper, and increasingly accurate estimations of the physical–environmental parameters of sustainable yield [95]. While the significant natural variation in aquifer physical–environmental settings would evidently impact planning needs and options to address highly localized to regional-scale GWS sustainability issues, by leveraging these innovations, more sustainable policies and decision-making standards to better sustain GWS may be created [96].

At the heart of GWS governance are its foundational legal doctrines and scientific assumptions. Courts and governments at multiple levels would need to make a definitive update of the Reasonable Use Rule relevant to the situational contexts of their GWS governance mandates. These considerations imply the abandoning the Underground Stream Doctrine in order to determine reasonable groundwater uses based on sustainable aquifer yield concepts. This contemplates (i) specification of volumetric thresholds for groundwater uses that avoid undesirable consequences on surface water bodies, aquifers, and dependent ecosystems in legal definitions; (ii) adding a temporal dimension to determining reasonable groundwater use, lowering use rates during droughts; (iii) considering the cumulative impacts of smaller-capacity wells over time [97], and (iv) differentiation of bulk water definitions for groundwater and surface water, with lower volumes set for the former given its relative scarcity and differing physical–environmental requirements of aquifers to maintain groundwater.

Restricting what is now considered "reasonable uses" of groundwater will likely require expansion of the Public Trust Doctrine [72]. However, applying public trust principles to govern groundwater use in the GLB has been rejected in the past due to fears over violating private property rights [98]. A 1983 California Supreme Court ruling (National Audubon Society vs. Superior Court 33 Cal.3d 419) provides a practical example for addressing this issue through sharing of public trust responsibilities with private landowners. To resolve a complaint by the National Audubon Society on the lowering Lake Meno's water level due to long-term pumping, the Court ruled that the public trust must be balanced between the Los Angeles Department of Water and Power and land proprietors. In so doing, it rationalized prior appropriation groundwater rights of landowners with the public lands and trust responsibilities of the government for conserving groundwater. By according public trust responsibilities to landowners, it effectively placed a duty on them to conserve groundwater below their lands.

Our third recommendation is to update economic policy tools to incentivize groundwater use efficiency. The structure of costs created by past GWS governance policies has resulted in groundwater being cheap and freely available to well owners, and insufficiently covering the cost of extraction and distribution of municipal water supply [59]. Regarding free trade agreements, these features have been embedded in the business models of industries attracted to the region [99]. While most GLB states/provinces have had voluntary guidelines for water use efficiency, mandatory standards and/or economic incentives should be considered to curtain groundwater overuse. Such incentives can include rebates for installation of efficient plumbing, promotion of judicious irrigation methods, and removing reducing block rates in municipal water supply tariff structures. Economic disincentives may also be considered, as illustrated in Ontario, who since the 1990s has set higher PTTW pricing for withdrawing bulk groundwater than for surface water, and progressively increases costs for PTTWs for higher groundwater volumes.

Looking back at the century-old arc of water resource governance in the GLB, there has been a tradition of collaboration and cooperation across political jurisdictions and government levels. The region's governments have established enduring institutions and more recently, taken steps to enshrine policies into law, suggesting growing political will to have stronger water resource safeguards. Multilevel institutions have also a long tradition of funding and conducting important scientific studies on the current state of the Basin's groundwater resources. With this trajectory, there can be some confidence in GLB continuing its transboundary governance evolution towards better science–policy alignment, to sustain "all waters" of the Basin, rising to the challenges of growing climate and growing human use stressors on vulnerable aquifers.

**Author Contributions:** Conceptualization, K.W.; methodology, K.W.; validation, K.W. and G.K.; formal analysis, K.W.; investigation, K.W.; data curation, K.W.; writing—original draft preparation, K.W.; writing—review and editing, K.W. and G.K.; visualization, K.W.; supervision, G.K.; project administration, K.W. and G.K.; funding acquisition, G.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** The research is supported by the Natural Sciences and Engineering Research Council of Canada.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

#### **References**

