**4. Conclusions**

While the value of ecosystem services has been widely recognized in the water industry, there has been limited investigation into the warning signals in the managemen<sup>t</sup> systems of such assets. Using a structured hazard analysis provides insight into the managemen<sup>t</sup> needs to ensure that stream buffers continue to perform as expected in the supply of safe drinking water.

This example provides a valuable test of how taking a highly systematic approach to identifying hazards using STPA can help to better understand managemen<sup>t</sup> requirements. Furthermore, developing a set of early warning signals and sensors using EWASP can

help us to understand the warning signals and sensors for the effective managemen<sup>t</sup> of natural assets. The uncertainty of outcomes can be a limiting factor when deciding between investing in catchment interventions and conventional water treatment infrastructure. However, the approach of using STPA and EWASP in combination provides a basis for being able to systematically design managemen<sup>t</sup> regimes for greater assurance of meeting the requirements for the safe and reliable supply of drinking water. Due to the systematic approach, this approach can be expanded as needed to encompass a range of different operational risks, such as the interlinkages with technical aspects (e.g., water treatment processes), and sociotechnical aspects, such as policy development.

The substantial number of early warning signs identified in this case would require significant resources to implement and measure. The methods used, are very helpful in identifying the hazards involved; however, they do not provide a means to assess the relative importance of the warning signs in the overall system. The validation, ranking, and selection of the final early warning signs warrant further research and investigation to assist WSPs in safely managing ecosystem services to protect drinking water quality.

**Author Contributions:** Conceptualization, H.C.M. and J.J.H.; methodology, H.C.M. and J.J.H.; formal analysis, H.C.M.; investigation, H.C.M.; resources, J.J.H.; data curation, H.C.M.; writing—original draft preparation, H.C.M. and J.J.H.; writing—review and editing, H.C.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

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

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data can be provided upon request.

**Conflicts of Interest:** The authors declare no conflict of interest.
