The common argument against the utilisation of SPIS is that this technology goes hand in hand with overexploitation and eventually depletion of limited water resources such as groundwater. Concerns are based on the following reasoning: SPIS lead to free pumping and hence an overexploitation of groundwater reserves is inevitable or at least very likely.
From a resource economist perspective, this argument is known as the Herder Problem or “the Tragedy of the Commons”  first described by Hardin in 1968: If there is a finite common-pool resource (e.g. groundwater) where it is difficult and costly to exclude potential users, this resource will eventually be exhausted because the rational individual will maximise his/her own utility rather than conserving the resource for the benefit of all. Meaning that an open-access resource will inevitably be over-exploited unless access and use of this resource are restricted by some form of governmental regulation or the allocation of property rights .
As an effect of the over-exploitation of a groundwater resource not only the environment but also the economy and society within the affected region have to suffer from several effects:
- Unsecure water availability through drying wells and springs increase the risk of crop failure;
- Aquifer salinization and seawater intrusion with long-term implications for agricultural productivity;
- Increased risk of conflicts between different users (e.g. farmers, domestic water supplier, industrial users);
- Environmental impacts on groundwater-dependent ecosystems, such as drying up of wetlands and river base flows .
The following argumentation will further show that all kinds of irrigation – and not just the solar powered one – face the same problems. The general principle is that the smaller the restrictions (lack of a mechanism for control of consumption or fee for use) of a water provision system, the greater the consumption will be . For that reason all irrigation in general requires the integration of principles of sustainable water management. Especially if groundwater regulation and protection in target countries is weak or even absent .
Definition of Groundwater
First, there are some general problems concerning knowledge on groundwater in principle.
Groundwater is usually defined as the water contained in underground reservoirs, whereas surface water bodies are rivers, lakes or reservoirs. The hydrological cycle links surface and groundwater and its dynamic nature makes categorical definitions problematic. Through seepage into the ground surface water can recharge aquifers e.g. when water seeps in the river bed or flood water percolates. The other way round, groundwater can become surface water through discharge into rivers, lakes and springs. So the flow of both systems overlap and they are not fully additive .
Besides the issues of precisely defining what groundwater is, there are major uncertainties on the volumes and spatial distribution of both groundwater recharge and withdrawals .Accurate data is missing  and as Morris et al.  argue, this chronic lack of data on groundwater conditions and trends results from an undervaluation of groundwater and the time lag between cause of the problem (e.g. over-abstraction) and effects (e.g. falling water levels).
Challenges of Groundwater Pumping
Arguments against the utilisation of SPIS concerning groundwater over-exploitation are actually arguments related to all water supply systems that run on groundwater in an ecologically unsustainable way. There are several issues that need to be considered when installing a water supply system of any kind (domestic and/or agricultural use) in order to operate in a way that the utilised water resource is not over-exploited. For the purpose of this work, the following arguments are related to the installation of groundwater-fed irrigation systems but could be generalised for other water resources and uses.
The evaluation of the water resource to be used should be the first step of any water supply project which should be done even before the conception of this project starts. The question here is e.g., if the water quality is appropriate for its planned usage. Possibly due to the already above mentioned lack of data, many studies fail to acknowledge and evaluate groundwater resources over the length of a project both in terms of quality and quantity which in consequence leads to the failure of the project .
The second reason why irrigation systems could be sized wrongly is that the water resource’s parameters are not taken into account. These parameters are the static and dynamic level of the water resource and its aquifer recharge (replacement) capacity. They depend on the composition of the geological substrata, rainfall patterns and topography and can undergo great variations. Because these parameters can be crucial for a good configuration of the system, capacity testing of the well prior to the configuration of the equipment is needed . In order to estimate the recharge capacity, the responsible authorities need to have as-accurate-as-possible data on the following:
- The total groundwater extraction by humans (via pumping) and springs,
- high resolution data on precipitation, evapotranspiration and runoff (land-use and vegetation/crop mapping of the groundwater basin helps to quantify these variables more exactly),
- hydrogeological data on the groundwater flow and underground storage characteristics (e.g. derived from pumping tests) .
Groundwater-fed irrigation does not only directly reduce the availability of groundwater, it also affects the local hydrological cycle. The surface soil moisture in irrigated areas is increased and thus evapotranspiration which increases the flux of the local hydrological cycle. Even though through seepage a part of the irrigation water flows back to the aquifer, groundwater pumping produces short-term decline in local groundwater levels. From the perspective of water balance, increases in evapotranspiration means that groundwater abstraction is greater than the replenishment and in the long run this can cause falling water tables. Groundwater pumping also affects the permafrost which causes a wide range of ecological problems .
The next detail that could lead to an over-exploitation of the groundwater resource is the lack of understanding of specific crop water requirements. If the amount of irrigation water needed is estimated incorrectly, the irrigation system is configured wrongly and the volume of groundwater abstraction might possibly be too great .
Domestic Water Use
Another very important aspect which has to be considered is that in rural contexts water supply systems for production and domestic consumption are usually combined . This results from the fact that because of natural purification processes much groundwater is of good quality what makes it a valuable source of potable water . Thus the level of demand has to be analysed with regards to that link.
The connection between water used for production and water for domestic consumption also plays a role in the so called repressed demand. This expression describes the increase in consumption when the initial situation in which there are obstacles in accessing a good or a service, like water, improves to a situation with easier access to the respective good or service. Like the installation of a groundwater-fed SPIS leads to the possibility of an increment in rural production and/or more convenience for the user. Very often users do not even know their repressed demand until he or she gains access to the previous scarce resource. Therefore real data or experience in order to forecast the increase in consumption is essential .
Another issue to be taken into account is the population growth of the benefited community. If in an area only one or a few communities receive electric power supply plus potentially potable water, it is probable that migration to those benefited communities will take place leading to a significant increase in the use of the provided services (electricity, water) .
When there is more than one water user in the area of influence of a well, the users will affect each other mutually by their respective water abstraction. In order to maintain a sustainable water withdrawal, a user agreement and a self-monitoring of the water abstraction must be in place .
Conflict of Irrigation
To argue that irrigation should not be performed at all is not a realistic plea. In a world that is expected to inhabit 9.8 billion people by 2050 (7.6 billion as of mid-2017 ), food security is challenged. One way to ensure supply could be irrigation as the FAO  notes: “The importance of irrigated agriculture cannot be overstated.” Irrigation accounts for 44% of total crop production on only 16% of the arable area . The area equipped for irrigation has been increasing, especially in developing countries. 1961 worldwide 142 million ha were equipped for irrigation, out of which 72.5% (103 million ha) were in developing countries. In 2005 in total 302 million ha were irrigated and developing countries accounted for 77.8% (235 million ha) . This increase was mainly done through engine-driven pumps .
With expanding irrigation comes the problem of increased water needs. At present 114 million ha of the area equipped for irrigation uses groundwater  and agriculture accounts for about 70% of the worldwide freshwater withdrawals . Hence irrigation is seen as one of the key factors behind global water scarcity.
In conclusion it can be stated that groundwater preserving water pumping requires regulation, enforcement of the rules and monitoring no matter which purpose the abstracted water serves (irrigation, drinking water, domestic use). As long as this is not ensured, aquifers will continue to shrink regardless of the energy source a water pump is running on.
It seems to be a vicious circle between increased demand for food and growing water scarcity caused by expanding irrigation. Following from the fact that abandoning the practice of irrigation is not an option, one should focus on shaping the current practice as sustainable as possible.
This energypedia article provides a comparison of solar powered, diesel powered and grid connected water pumping sytems.
- ↑ 1.0 1.1 Hardin, G., 2009. The Tragedy of the Commons. J. Nat. Resour. Policy Res. 1, 243–253. http://dx.doi.org/10.1080/19390450903037302.
- ↑ 2.0 2.1 2.2 2.3 GIZ, FAO, 2017. Toolbox on Solar Powered Irrigation Systems (SPIS): Information and Tools for Advising on Solar Water Pumping and Irrigation. Safeguard Water. URL https://energypedia.info/wiki/Toolbox_on_SPIS.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Fedrizzi, M.C., Ribeiro, F.S., Zilles, R., 2009. Lessons from field experiences with photovoltaic pumping systems in traditional communities. Energy Sustain. Dev. 13, 64–70. doi:10.1016/j.esd.2009.02.002. http://www.sciencedirect.com/science/article/pii/S0973082609000210.
- ↑ 4.0 4.1 4.2 Siebert, S., Burke, J., Faures, J.M., Frenken, K., Hoogeveen, J., Döll, P., Portmann, F.T., 2010. Groundwater use for irrigation: A global inventory. Hydrol Earth Syst Sci 14, 1863–1880. doi:10.5194/hess-14-1863-2010. https://www.hydrol-earth-syst-sci.net/14/1863/2010/.
- ↑ Vallée, D., Margat, J., Eliasson, Å., Hoogeveen, J., Faurès, J.-M., 2003. Review of world water resources by country (No. 23), Water report. FAO, Rome. ftp://ftp.fao.org/agl/aglw/docs/wr23e.pdf.
- ↑ Gleeson, T., Wada, Y., Bierkens, M.F.P., van Beek, L.P.H., 2012. Water balance of global aquifers revealed by groundwater footprint. Nature 488, 197–200. doi:10.1038/nature11295. http://www.nature.com/doifinder/10.1038/nature11295.
- ↑ 7.0 7.1 7.2 Closas, A., Rap, E., 2017. Solar-based groundwater pumping for irrigation: Sustainability, policies, and limitations. Energy Policy 104, 33–37. doi:10.1016/j.enpol.2017.01.035. http://www.sciencedirect.com/science/article/pii/S0301421517300459.
- ↑ 8.0 8.1 Morris, B.L., Lawrence, A.R.L., Chilton, P.J.C., Adams, B., Calow, R.C., Klinck, B.A., 2003. Groundwater and its susceptibility to degradation: A global assessment of the problem and options for management, Eary warning and assessment report series. United Nations Environment Programme, Nairobi, Kenya. http://nora.nerc.ac.uk/19395/.
- ↑ Yu, Y., Liu, J., Wang, H., Liu, M., 2011. Assess the potential of solar irrigation systems for sustaining pasture lands in arid regions: A case study in Northwestern China. Appl. Energy 88, 3176–3182. doi:10.1016/j.apenergy.2011.02.028. https://bit.ly/2xjfXLA .
- ↑ 10.0 10.1 United Nations, 2017. World Population Prospects: The 2017 Revision, Key Findings and Advanced Tables (Working Paper), ESA/P/WP/248. Department of Economic and Social Affairs, Population Division, New York. https://esa.un.org/unpd/wpp/Publications/.
- ↑ 11.0 11.1 11.2 FAO, 2012. World Agriculture Towards 2013/2050: The 2012 Revision (No. 12–3), ESA Working Paper. Global Perspective Studies Team. http://www.fao.org/docrep/016/ap106e/ap106e.pdf.
- ↑ Abu-Aligah, M., 2011. Design of photovoltaic water pumping system and compare it with diesel powered pump. Jordan J. Mech. Ind. Eng. 5, 273–280. https://bit.ly/2AlY0tw .