Concentrating solar power plants (CSPPs) are considered to be particularly respectful of the environment but under Mediterranean climate where surface water scarcity is a key issue, these types of electrical plants usually require groundwater for their cooling towers and use the same aquifers to discharge their salinized effluents. This study analyses de Spanish case, where fifteen out of the fifty active CSPPs use groundwater directly, four discharge their effluents to infiltration ponds and forty-three to surface watercourses most of which recharge underlying aquifers. The volume of water withdrawn and discharged varies greatly among similar plants. The salinity of the effluent exceeds 2.5 times that of the withdrawn water in half of the plants and it may alter the current or potential use of the water turning it unsuitable for drinking or even for irrigation. There is a risk that the impact on groundwater can be extended to related ecosystems such as wetlands. This can become a serious environmental problem, but specific impacts on groundwater are often overlooked in environmental impact assessments of CSPPs and no research on the matter has been reported so far. Other legal and political implications of CSPPs are further discussed.