A New Method of Obtaining Water from Water Storage Tanks in a Crisis Situation Using Renewable Energy

Abstract

Background: During a crisis situation, water supply systems stop functioning properly. It is necessary to obtain water from sources other than basic ones (reserve water intakes, water storage tanks, bottled water). Methods: We aim to determine the water demand in a crisis situation based on current European guidelines and determine the time to cover the demand for water from water storage tanks during a crisis situation. Results: An installation for drawing water from a water storage tank, which includes water disinfection using a UV lamp, is necessary. Continuity of operation is guaranteed by the use of a photovoltaic installation independent of the power grid. The amount of water stored in water storage tanks is enough to meet the basic needs of the population for up to several weeks. Conclusions: The use of a UV lamp with an independent backup power supply allows maintaining the microbiological purity of water during a long-term crisis situation.

1. Introduction

A crisis situation, according to [1,2], is a situation that negatively affects the level of safety of people, property or the environment, causing significant limitations in the operation of relevant public administration bodies due to the inadequacy of the forces and resources at their disposal. Crisis situations in water supply systems include [3,4,5,6,7,8]:

• Large-scale failures of electric power systems—power blackouts;
• Water contamination that conventional treatment processes cannot remove;
• Extreme weather phenomena, flood;
• Cyberattack on IT systems, including automatic control of the water treatment process;
• Failures of key water mains and pumping stations;
• Secondary microbiological contamination of water in the water supply network or water storage tanks;
• Military conflict.

During normal operation, water is supplied via water supply systems. During a crisis situation, water systems stop functioning properly. There is a drop in pressure in the water supply network, and water is not delivered to consumers or water of a quality inconsistent with applicable regulations is supplied. The risk of undesirable events in water supply systems is constantly increasing [9,10]. This is related to both environmental and anthropotechnical threats. According to a report by WWF and the Living Rivers Europe Coalition [11], 90% of river basins studied in various EU countries will still be unhealthy by 2027. This makes it necessary to use advanced, energy-intensive water treatment technologies. These systems require a 24/7 supply of electricity. A power blackout would therefore prevent the proper functioning of water supply systems. Energy security must be considered in a broad regional and cross-border context [12]. Risk management in water supply systems and related risk mitigation measures are required by Directive (EU) 2020/2184 [13] and standards EN 15975-1 [14] and EN 15975-2 [15].

Access to safe drinking water is one of the priorities in the event of a crisis situation. For this reason, research is being carried out to look for ways to obtain drinking water in a crisis situation. In the initial phase of a crisis situation, each reserve water intake should be treated as potentially contaminated. Only the results of microbiological, physicochemical and toxicological tests of water allow for the assessment of suitability for consumption [16]. Work [17] presents a number of solutions for water treatment in crisis conditions. Possibilities of unconventional obtaining drinking water are also being explored [18,19]. In crisis situations, water should be rationed. It is possible to use treated water accumulated in water pipes [3]. During a crisis situation, water supply may be provided using:

• Underground reserve intakes;
• Water collected in water storage tanks;
• Bottled or bagged water;
• Vehicles for water distribution based on own resources and cooperation agreements with external entities.

Operational practice shows that the vast majority of water supply companies do not have reserve intakes in an operational condition; therefore, the possibilities of water supply outside the water supply network are limited [20]. It is therefore necessary to have a container of drinking water from which water can be distributed in a crisis situation. Water storage tanks are usually equipped with a water supply and discharge pipe, an overflow and a water drain. There are known solutions that enable water to be drawn into vehicles. This can be achieved using an appropriate system of pump-powered pipes and vehicle-filling nodes. It is also possible to draw water from a hydrant located below the water storage tank. None of the known solutions guarantees safe consumption of water collected in water storage tanks during a power blackout for several days. Long-term accumulation of water causes it to be exposed to secondary contamination [21,22]. Water storage tanks hold up to several thousand cubic meters of water, which is an important source of water during the energy crisis. However, there is no known system enabling its safe use in a crisis situation, especially a power blackout.

This work focuses on the crisis situation related to power blackouts. When a crisis situation occurs, people start to behave irrationally and panic [23]. The natural behavior in the face of great anxiety is to accumulate supplies that will allow for survival in the crisis. In the event of a power blackout and, consequently, a progressive drop in pressure in the water supply network, people will start filling containers, pots and bathtubs to ensure a supply of water. This causes a faster drop in pressure in the water supply network. Water storage tanks, even if filled, will only slow down the pressure drop process. Water consumption will be higher than usual, and the tanks will empty within a few or a dozen or so hours. Then, the only solution is to distribute water outside the water supply network. It is then necessary to have a water source for water tankers. According to the developed concept, one of the water storage tanks should be cut off from the water supply network, and the water collected in it should be a source of water for water tankers.

The aim of this research was to determine the actions that should be taken to increase the possibility of distributing drinking water among the population affected by the crisis using the resources owned by the water supply company. The most critical element of the water supply system in a crisis situation is access to alternative water sources, which, in order to be used for the needs of the population, must be maintained in a technically efficient condition. The emergency water source should also be microbiologically safe and independent of electricity supplies. The developed solution solves problems that can be classified as technical and social. The solution includes water disinfection using a UV lamp, which guarantees the removal of microorganisms that may grow in the stored water. Continuity of operation is guaranteed by the use of a photovoltaic installation independent of the power grid.

The aim of the work is to present the concept of a new installation that will enable the use of water accumulated in water storage tanks to supply water to populations in crisis situations, e.g., a power blackout, when the water pressure in the water supply network drops and residents have no access to tap water. Photovoltaic installations are already used in water supply systems to power water pumping stations [24]. Solutions allowing the use of renewable energy in water supply systems have been increasingly used in recent years. Previously conducted research focuses mainly on the use of solar energy, wind energy, hydropower and hybrid systems [25]. Commonly known solutions include the use of pump systems powered by renewable energy (a photovoltaic (PV) array and wind generator) used to irrigate agricultural areas [26]. Pumping systems based on solar energy are used especially in dry areas to irrigate small farms [27]. A photovoltaic water pumping system can be used to draw water from a well or other reservoir [28,29]. The tap water pumping system, if conditions are appropriate, can be powered by a hybrid wind and photovoltaic energy supply system. Such a system can work with a spare battery [30]. A solar-powered water pumping system may consist of photovoltaic panels, a battery bank, inverter, pump and reservoir for irrigation purposes [31]. The innovativeness of the developed solution consists of:

• Using a photovoltaic installation to power the pump and draw water from water storage tanks located in the water supply network in a crisis situation;
• Using a photovoltaic installation to power a UV lamp in a crisis situation,
• Using a power source switch—automatic switching of loads from the primary power source to the reserve power source (and vice versa) in the event of a failure in the three-phase network;
• Creating a reservoir of clean and safe water that can be used to meet the basic, physiological needs of the affected population for up to several weeks, regardless of the supply of electricity from the grid.

The main advantage of the proposed method compared to the existing ones is the development of technical solutions for guaranteeing resources for water supply in crisis situations. For this purpose, water stored in water storage tanks will be used. Previous methods focused on the possibility of obtaining water in quantitative terms. The use of the developed method makes it possible to obtain microbiologically safe water. The microbiological condition is the most important feature of water health and safety. The use of a UV lamp is to ensure appropriate microbiological quality. The effectiveness of this solution is confirmed by a number of studies [32,33,34]. At the current stage of research, there is no need to conduct additional analyses in this area, especially since water in water supply tanks must meet the requirements for water intended for human consumption specified in the Directive [2]. The water in water storage tanks is clear and does not contain significant concentrations of pollutants that most affect the effectiveness of UV rays. Thanks to the use of a UV lamp, the water becomes safe for humans. This study also presents a quantitative assessment of the possibility of meeting the needs of the affected population based on water obtained from water storage tanks and distributing it outside the water supply network. For this purpose, calculations of the crisis demand for water were carried out.

This work contributes to the development of knowledge regarding the possibility of delivering water to recipients in a crisis situation. The developed installation can operate independently of the electricity supply from the grid, thanks to the use of a renewable energy source with a photovoltaic installation, backup battery and a power source switch. Such a solution has not been considered so far. Another novelty of this study is the creation of the possibility of disinfecting water taken from a water storage tank, which is particularly important if the age of the water exceeds 3 days. This work is of great practical importance because it contributes to solving the problem of the availability of drinking water after long-term power failure. This research also has several other important benefits, including reducing stress among affected populations through the supply of clean, microbiologically safe water.

2. Materials and Methods

2.1. Characteristics of the Research Object

The research was carried out for a water supply system located in south-eastern Poland. In the city covered by the study, there are 19 network water storage tanks with a total capacity of 53,045 m³. However, only 12 of them are in operation, with a total volume of 49,533 m³. Figure 1 shows the location of water supply reservoir complexes in the city.

The water supply system covered by the study is characterized by a very high level of water reserves in the water supply network. The water collected in the system exceeds the level of the average daily water consumption. The distribution of tanks in the water supply network is even. Diversification of water resources is at a satisfactory level. During normal operation, water supply tanks perform their function very well, increasing the reliability of water supply.

The use of the developed installation requires decommissioning at least one water storage tank. Appropriate arrangement of water supply tanks allows one tank to be turned off without significant damage to the operation of the water supply system. It is proposed to use the water collected in the water storage tank included in tank complex no. 3 with a capacity of 15,000 m³. It is a newly opened water tank with a large capacity, the adaptation of which to the water intake by the new installation will require the smallest investment outlays. It is one of the largest water storage tanks in Poland.

2.2. Demand for Water in Crisis Situations and Possibility of Obtaining Water from Water Storage Tanks

Determining the water demand is a fundamental condition for dimensioning the installation for water abstraction from water storage tanks. Water demand in a crisis situation was determined in accordance with current guidelines [35,36,37]:

• Individual physiological water demand: q_p = 2.5 dm³/person per day;
• Individual minimum demand for drinking water: q_m = 7.5 dm³/person per day (human physiology and basic hygiene practices);
• Individual necessary demand for drinking water: q_n = 15 dm³/person per day (human physiology, basic hygiene practices and basic cooking).

The demand for water in a crisis situation was determined from the formulas:

$$Q_p=q_p·NR$$

(1)

$$Q_m=q_m·NR$$

(2)

$$Q_n=q_n·NR$$

(3)

where:

-

Q_p—water demand in a crisis situation (physiological) [m³/day];

-

Q_m—water demand in a crisis situation (minimal) [m³/day];

-

Q_n—water demand in a crisis situation (necessary) [m³/day];

-

q_f, q_m, q_n—individual water demand in a crisis situation (q_p = 2.5 dm³/person per day; q_m = 7.5 dm³/person per day; q_n = 15 dm³/person per day);

-

NR—the number of residents.

Calculations of water demand in a crisis situation are presented in

Table 1. Demand for water in a crisis situation for the city.

The Number of Residents	Qn [m3/day]	Qm [m3/day]	Qp [m3/day]
195,840	2937.6	1468.8	489.6

. The total number of city inhabitants was taken into account.

The assessment of the possibility of obtaining water from the water storage tank was made based on the quotient of the volume of water collected in the water storage tank and the crisis demand for water. The calculations were carried out with different fillings of water storage tanks. Time to cover the demand for water from water storage tank during a crisis situation:

$$t_p=\frac{Q_{zb}}{Q_p}$$

(4)

$$t_m=\frac{Q_{zb}}{Q_m}$$

(5)

$$t_n=\frac{Q_{zb}}{Q_n}$$

(6)

where:

-

t_p—time to cover the demand for water from water storage tank (physiological water demand) [day];

-

t_m—time to cover the demand for water from water storage tank (minimum demand for drinking water) [day];

-

t_n—time to cover the demand for water from water storage tank (necessary demand for drinking water) [day];

-

Q_zb—the amount of water collected in the water storage tank (four variants were assumed: tanks are 100%, 75%, 50% and 25% full) [m³].

Water supply tanks must have the ability to draw water from water tankers. A key aspect to ensuring an adequate amount of water in a crisis situation is having an appropriate number of vehicles to transport water from water storage tanks to distribution sites. The desired state is to achieve water supplies at the level of meeting physiological needs (assuming 10 courses per day).

3. The Concept of Obtaining Water from Water Storage Tanks in a Crisis Situation

3.1. Characteristics of the Developed Installation for Drawing Water from a Water Storage Tank

The installation for drawing water from a water storage tank in a crisis situation is characterized by the fact that a water pipe is mounted to the water storage tank, with a pump on it, which can be powered using a power source switch (automatic switching of the reserve) via the mains power supply or photovoltaic panels and battery. A UV lamp is installed on the branch of the water pipe, which can also be powered using a power source switch (automatic reserve switching) via the mains power supply or photovoltaic panels and batteries. The water pipe is ended with a hydrant cap. The installation has a bypass, thanks to which water can be taken from the water supply tank by gravity.

The new installation enables the use of water accumulated in water storage tanks. Water can be collected using a delivery hose to a water tanker or other container. The use of a UV lamp with an independent backup power supply allows us to maintain the microbiological purity of water even during a power blackout. The appropriate efficiency of the installation covered by the invention is ensured using a pump with an independent reserve power supply. Water can be drawn from a water supply tank both during a crisis and during normal operation. The developed installation is shown in Figure 2.

The installation for drawing water from a water supply tank includes a water pipe (1), which is led from the water storage tank (2) and on which the pump (3) is mounted. The input of the power cable (4) of the pump (3) is connected to the output of the power source switch (5). The first input of the power source switch (5) is connected to the mains power output (6), and the second input of this power source switch (5) is connected to the output of the inverter (7), the input of which is connected to photovoltaic panels (8). The inverter (7) is connected to the battery (9), which stores energy for the duration of the power blackout. A UV lamp (10) is attached to the water pipe (1), the input of which is connected to the output of the charger (11), the input of which is connected to the power source switch (5). Water pipe (1) is closed with a hydrant cap (12). Photovoltaic panels (8) convert solar energy into electricity and enable emergency power supply of the UV lamp (10) and the pump (3). During normal operation, the pump (3) and UV lamp (10) are powered by the electricity network. The inverter (7) converts the direct current generated in the photovoltaic panels (8) into alternating current used in the pump (3) and the UV lamp (10). There are gate valves on water pipe (1). The entrance of the bypass pipe (13) is attached to the water pipe (1), before the entrance of the pump (3), the outlet of which is attached to the water pipe (1) after the outlet of the pump (3). The bypass pipe (13) allows the water to bypass the pump (3), thanks to which the water can be drained from the water supply tank (2) by gravity.

The energy converted by the photovoltaic panel can be estimated using the following formula [26]:

$$E_{ph}=P_r{F}_0\left(\frac{G_{eff}}{G_0}\right)P_C$$

(7)

where:

• P_r—the performance ratio (average value 0.72 or 0.75);
• F₀—a factor that accounts for losses;
• G_eff—the effective instantaneous incident irradiance (W∕m²);
• G₀—the irradiance under standard conditions (1000 W∕m²);
• P_C—the nominal power under standard conditions as provided by the manufacturer (W).

The dimensions of the objects included in the developed installation, i.e., pump, UV lamp, photovoltaic panels, depend mainly on the water flow. The power and capacity of the equipment may, therefore, vary in different water systems and tanks. The amount of water that can be taken from the water supply tank should not be lower than 10 dm³/s (36 m³/h; 864 m³/day), and for this amount, it is indicated what power and type of equipment can be used:

• UV lamp—nominal flow at transmission T₁₀ = 95%, dose of 400 J/m² is 40 m³/h; UV radiator power: 325 W; DN100/220; (TMA, Białostoczek, Poland);
• Vertical, multistage centrifugal pump; efficiency: Q = 37.2 m³/h; height: H = 21.36 m; pump efficiency: 72.8%; power 3356 W; (Grundfos, Bjerringbro, Denmark);
• Monocrystalline solar PV modules with a peak power of 420W. One PV unit can process 840 kWh/year; module technology: 144 Half-Cut cells; efficiency: 210.19 W/m²; module efficiency: 21%. It will be necessary to install 12 such modules, creating a system with a total power of 5 kW; (Trina Solar, Jiangsu, China);
• Hybrid Solar Inverter 5 kW; nominal DC Voltage: 48V DC; Maximum PV Array Open Circuit Voltage: 450 V DC; support parallel; (DAXTROMN, Hongkong, China);
• Battery—low-voltage energy storage; capacity 100 Ah; energy: 20.37 kWh; maximum continuous current: 90 A; nominal voltage: 51.2 V; (Kon-TEC, Rzeszow, Poland);
• A power source switch—automatic switching of loads from the primary power source to the reserve power source (and vice versa) in the event of failure in the three-phase network; power supply 3 N 400 V/230 V 50 Hz; degree of protection: IP 20; (POLLIN, Warsaw, Poland).

The technical parameters of the installation refer to a water storage tank with a capacity of 15,000 m³ located in the analyzed water supply system. A water storage tank with this capacity can be the main source of drinking water in a crisis situation for a long time. This is a universal set of equipment enabling the consumption of safe drinking water in the amount of approximately 10 dm³/s. The installation can be used for various network water storage tanks that collect water in an amount that allows us to cover crisis demand for drinking water for a period of at least several days.

The cost of implementing the developed installation is currently estimated at approximately EUR 20,000. The cost shown may vary by location. The payback period for the photovoltaic installation is not specified in this article. This issue was abandoned due to the specific nature of the installation’s operation, i.e., supply of energy at the moment of voltage loss in the primary source of supply. The operation of the developed installation is periodic. Its main goal is not to reduce grid energy consumption. It should be emphasized that in the case of investments that have a significant impact on human safety, the cost of the project is not the most important thing.

The developed water intake installation allows for obtaining water suitable for consumption in the required quantity, i.e., 864 m³/day in continuous operation, which is greater than Q_p = 489.6 m³/day (physiological water demand in a crisis situation). Maintaining adequate supplies of drinking water is one of the most important elements of logistics management in crisis situations. The developed installation enables the collection of water subjected to a natural disinfection process. Water is collected into a water tanker or other container and distributed among residents during a crisis situation such as low pressure in the water supply network. The amount of water that can be collected using this new installation is 10 dm³/s, and it depends mainly on the amount of water in the water tank, the power of the photovoltaic panel installation, the capacity of the batteries and the efficiency of the pump. The amount of water drawn is regulated by the operation of the pump and the valves installed in the water pipe. The installation can be used both in network water tanks and in clean water tanks. Residents who do not have access to tap water receive microbiologically safe water obtained from the installation, which is ultimately distributed at points located throughout the city. Water is withdrawn until it is exhausted in the water storage tank. During normal operation of the water storage tank, the installation is usually not in operation or the pump and UV lamp are powered from the mains. In the event of a power blackout, switching occurs using the power source switch. The pump and UV lamp are powered by electricity obtained from photovoltaic panels. In the event of a long-term power blackout, the pressure in the water supply network decreases. It is necessary to obtain drinking water and distribute it outside the water supply network. After starting the pump and the UV lamp, it is possible to draw water through the hydrant cap and fill the water tankers.

3.2. Possibility of Meeting the Needs of the Affected Population Based on Water Obtained from Water Storage Tanks

Facilities such as water storage tanks and water treatment plants (WTP) are perfect for cooperation with photovoltaic installations. Photovoltaic panels can be placed, among others, on the roof of large water storage tanks or in the WTP area. These are large installations which, if they serve water supply systems for agglomerations, may have a capacity of up to several MW. The electricity generated by photovoltaic panels usually powers water intake pumps, WTP equipment and network pumps. Photovoltaic installations cover part of the water company’s demand for electricity. The use of photovoltaic panels improves the city’s drinking water supply during emergencies. This solution is increasingly used in the EU, which is consistent with the EU energy strategy. The main characteristic feature of the proposed method, compared to the existing ones, is the possibility of disinfection and water intake into water tankers regardless of the power supply from the power grid. Water is collected through an additional system of pipes, which is adapted to water collection by water tankers.

The task of conventional photovoltaic power plants used in the WTP is to increase the production of electricity for their own needs. In this way, the costs of purchasing energy from the grid are reduced. The developed method focuses on maintaining the continuity of operation of the developed installation regardless of external conditions. Below are the advantages of the proposed method compared to conventional installations used in WSS:

• The developed photovoltaic installation powers a separate water intake installation including a pump and a UV lamp; low installation power is required (5 kW) compared to conventional solutions powering complex pump systems and water treatment devices;
• It is an emergency power system; the aim is to provide electricity in the moments of voltage failure in the primary source of supply; this is of strategic importance to ensure the continuity of the supply of clean and safe water to people in a crisis situation;
• Use of battery in the developed installation (20.37 kWh)—in the event of a power failure from the primary source, the energy storage facility can release the stored energy for a specified period of time (approximately 5 h);
• Energy can be taken by the battery directly from a renewable energy source (a set of 12 photovoltaic modules creating a system with a total power of 5 kW), which increases the ecological aspect of the investment;
• No need to provide an additional power source, such as a generator.

When the water supply system does not have the capacity to supply water in a crisis sufficient to meet the basic needs of the population, one of the reservoirs is cut off from the water supply network. The accumulated water supply will be used to meet the basic needs of the population (q_p = 2.5 dm³/person per day) for a period of several weeks. The developed installation is launched. The pump and UV lamp start working. They are powered by a photovoltaic installation. Water is collected in water tankers, which distribute the water to water distribution points that are evenly distributed throughout the city. These points are easily accessible to residents near public buildings (schools, offices, etc.). The general framework of the method is shown schematically in Figure 3.

In the event of a complete lack of water supply to the city, water storage tanks may be the source of water in the first few days of the crisis. The time to cover the physiological, minimum and necessary water demand in a crisis situation was determined for four variants, assuming that the tanks are 100%, 75%, 50% and 25% full. In fact, the time needed to cover water demand will depend on the current water level in individual reservoirs. The volume of water collected in a selected water storage tank is shown in

Table 2. Time to cover water demand during a crisis.

Demand for Water in a Crisis Situation	Time to Cover Water Demand [Days]
The volume of water in the water storage tank: 15,000 m3 (100% filling)
Qp = 489.6 m3/d (physiological)	30.64
Qm = 1468.8 m3/d (minimal)	10.21
Qn = 2937.6 m3/d (necessary)	5.11
The volume of water in the water storage tank: 11,250 m3 (75% filling)
Qp = 489.6 m3/d (physiological)	22.98
Qm = 1468.8 m3/d (minimal)	7.66
Qn = 2937.6 m3/d (necessary)	3.83
The volume of water in the water storage tank: 7500 m3 (50% filling)
Qp = 489.6 m3/d (physiological)	15.32
Qm = 1468.8 m3/d (minimal)	5.11
Qn = 2937.6 m3/d (necessary)	2.55
The volume of water in the water storage tank: 3750 m3 (25% filling)
Qp = 489.6 m3/d (physiological)	7.66
Qm = 1468.8 m3/d (minimal)	2.55
Qn = 2937.6 m3/d (necessary)	1.28

. Out of 12 active network water storage tanks, 1 was taken into account. The remaining tanks will supply the water supply network and reduce the pressure drop in the water supply network.

The physiological demand for water can be covered from the water storage tank for a period from 7.66 days to 30.64 days (depending on how full the tank is). The recommended water retention time in a water supply tanks is 40 h, and the maximum permissible age of water is 72 h (3 days). Therefore, it is necessary to disinfect water taken from water storage tanks if the water is stored there for more than 3 days. The developed installation uses a UV lamp with an independent backup power supply. This makes it possible to maintain the microbiological purity of the water and allows it to be distributed among residents. The desired state is defined as achieving the ability to provide water supplies at the level of meeting physiological demand. It is necessary to maintain an appropriate number of means for transporting water outside the water supply network, i.e., water tankers, containers.

If it is necessary to supply water to residents in a minimum amount (7.5 dm³/person per day), the water supply in the tank will range from 2.55 days to 10.21 days (depending on how full the tank is). If water is consumed in the necessary amount (15 dm³/per day), the water will last for a period from 1.28 days to 5.11 days (depending on how full the tank is). In such a case, the barrier limiting the possibility of distributing water from the water storage tank will be the number of means of transport at the disposal of the water supply company.

4. Conclusions

Progressing climate change, the growing threat of cyberterrorist attacks, as well as the occurrence of failures in the energy generation and transmission infrastructure make it necessary to adapt critical infrastructure to function in crisis conditions, including power blackouts. This also applies to water supply systems, which are necessary for the proper functioning of society and the state. Energy storage systems coupled with a photovoltaic installation allow us to secure the continuity of system operation during a power blackout.

This paper presents a new method of collecting water from a water storage tank in a crisis situation. The proposed installation has an independent renewable energy source. This increased the safety of the water supply. The use of a UV lamp with an independent backup power supply allows us to maintain the microbiological purity of water during a long-term crisis situation. This is very important because in the event of a crisis situation and the disconnection of basic power sources, the supply of water in the water supply network runs out very quickly. The proposed method of abstracting water from a water storage tank outside the water supply network will provide people with drinking water, necessary to survive the crisis. This will avoid the risks associated with people drinking dirty water from unreliable sources.

This study calculated the time needed to cover the demand for water from water storage tanks in a crisis situation. The amount of water stored in water storage tanks is enough to meet the basic needs of the population for up to several weeks. It is a very important source of water for people in the event of a natural or man-made disaster. The obtained water must be distributed throughout the supply area by road transport. The main limitations of the developed method of collecting water from water tanks include the fact that the installation must use water that does not contain significant concentrations of pollutants (it must be clear). The method is therefore suitable for additional disinfection of already treated water. Another limitation is the need to have an appropriate number of means of transporting water from water storage tanks to water distribution points. In this respect, cooperation with external entities is necessary, i.e., neighboring water supply companies, fire brigades, etc. Independently maintaining 5-6 vehicles to transport water in a crisis situation has no economic justification and is, in practice, unrealistic. This number of vehicles would ensure a daily water supply at the level of physiological water demand in a crisis situation. Before implementing the installation in the target water supply system, its basic subsystems must be confirmed in laboratory conditions.

The presented installation for drawing water from water storage tanks in a crisis situation using renewable energy has a very large implementation potential. The main potential recipients of the project results are water supply companies. It is necessary to ensure continuity of operation not only in normal conditions but also in crisis conditions. The implementation of the presented solution allows for the creation of an alternative to the currently used methods of water supply in crisis conditions based on underground water intakes. The results obtained allow for the refinement of Crisis Management Plans at various levels of state administration. The logistics process for managing water supply in crisis can be improved. The research topic covered is part of a broad area related to the critical infrastructure of cities, sustainable development, quality of life and security. The developed solution is an original and new combination of known elements of water supply and energy systems. The installation can be manufactured repeatably in various water supply companies based on the presented solution description.

Further research should include the impact of shutting down selected water storage tanks on the hydraulics of the water supply network in a crisis situation. It is also necessary to determine the correlation between the capacity of the water supply tank, the pipe diameter and the photovoltaic installation.

5. Patents

There are patents resulting from the work reported in this manuscript. The Patent Office of the Republic of Poland states that on 2 January 2024, an application for a patent for the invention “Installation for drawing water from a water supply tank” was accepted. The application was marked with the number P.447449.