Summer Water Demand and Seawater Intrusion on the Eastern Mediterranean Coast

Seawater intrusion is a balance problem. In a coastal aquifer, fresh groundwater flows seaward and keeps denser seawater offshore. When pumping lowers the freshwater head, the freshwater–seawater interface moves inland. Here abstraction has already pushed intrusion 2.5 km inland and raised chloride above 400 mg/L in three wells, which is why they were closed.

The seasonal pattern makes it worse. Annual demand is 180 million m³, but July–August demand is 1.8 times the winter average because residents, tourists and hotels use more water. The summer population rises by 35%. Pumping peaks exactly when natural recharge is lowest - the Mediterranean summer is dry - so the water table is drawn down further. Agriculture uses 55% of supply, mainly citrus and vegetables, and also irrigates heavily in summer.

The result is a feedback loop: summer peak pumping lowers the water table, seawater moves inland, wells become saline and are closed, and the remaining wells must pump harder. The aquifer is being mined, not managed. Any supply option must address the summer peak, not only the annual total.

Desalination. A 100 million m³/year plant is a large, climate-independent supply. It can replace about 55% of current annual demand and reduce groundwater abstraction. But it is energy-intensive, expensive, and produces brine that may affect seagrass if poorly discharged. It also runs at a constant output, while demand peaks in summer; without storage, the plant does not solve the seasonal peak by itself. It may encourage continued high demand unless paired with tariffs.

Wastewater reuse plus summer tariff. Reuse can supply agriculture, which uses 55% of water, and so free freshwater for households and hotels. It is cheaper per m³ than desalination in many cases and reduces nutrient pollution. But farmers say the reuse water is too saline; without salinity management and leaching, citrus yields may fall. A summer tariff directly targets the peak and can fund leak repair and reuse infrastructure, but hotel owners oppose it and tourism is seasonal and price-sensitive.

Neither option alone is sufficient. Desalination without demand management is costly and does not fix the summer peak. Reuse without salinity control may fail in agriculture. A tariff without alternative supply may hurt tourism. The evaluation should compare cost per m³ of firm supply, energy, brine and salinity risk, and speed of implementation.

Recommended mix: desalination at a scale below 100 million m³/year in the first phase, combined with wastewater reuse for agriculture and a seasonal tariff. A smaller first plant - say 60–70 million m³/year - reduces brine and energy risk while testing demand response. Reuse should be targeted at fodder, orchards and industrial crops, with salinity monitoring and leaching; not all citrus should receive it. The summer tariff should be tiered, with exemptions or efficiency support for small hotels and low-income households.

Aquifer protection: establish a coastal well-field monitoring network for chloride, water level and abstraction; set a minimum freshwater head and a maximum abstraction rate; relocate or deepen the most threatened wells; and require metering of all agricultural and municipal pumps. Identify a managed aquifer recharge site using treated stormwater or excess desalinated water in winter.

Sequencing: first metering and leak reduction, because they are fast and cheap; then reuse and tariff, which reduce summer abstraction; then desalination, which adds firm supply. This order avoids building a large plant to supply water that could have been saved. Protect the aquifer by treating it as a buffer, not as a primary source during the summer peak.