The conclusions from the planning model are that we can protect the groundwater resources by adopting higher restrictions on salinity levels, so more treatment and desalination is needed. This is followed by higher treatment and supply cost. The main points are that:

• Supplying desalinated sea or brackish water is a solution for quantity and quality of water;

• Irrigation with wastewater decreases supply costs but increases salinity;

• All supply alternatives should be considered regarding their impact on ground-water salinity as well as on economic cost.

The conclusions from calculating the costs of improving the threshold chloride levels in the water supplies to city and/or agriculture or the steady-state levels in the aquifer are the following:

• Desalination of brackish water involves the lowest costs;

• Desalination of National Carrier water is effective when there is large-scale use;

• Desalination of wastewater is significant for maintaining the chloride concentration threshold in water for agriculture;

• Desalination of seawater is recommended when it makes an important contribution to maintaining the national water balance;

• Most importantly, we conclude that the economic cost of improving the quality of the supplied water and of the aquifer water should be considered in decision making.

To summarize, climate change increases the stress on water sources, and overexploitation of groundwater sources results in aquifer contamination and increased salinity. Therefore, alternative water sources should be developed, including treated wastewater use in agriculture and desalination of sea water for domestic water use. Restrictions on water quality are needed to ensure sustainable groundwater management, but these restrictions involve increased costs. National decision makers should take into account both the environmental impacts and the economic costs of different water supply sources, including their impacts on groundwater resources as well as the impacts of different policies on climate change.

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