Aside from humanitarian decency, there are ample pragmatic reasons for Israel to be concerned. Every day, 3.5 million cubic feet of sewage pours into the Mediterranean. Israel’s own drinking water supply is increasingly dependent on seawater desalination. One of its largest facilities, in Ashkelon, is just a few miles north along the coast from Gaza. Erecting a fence can prevent terrorist infiltration, but it can’t stop the flow of feces.

This sewage crisis is only the most acute manifestation of Gaza’s hydrological nightmare. Pressure on water resources long since became unsustainable. Historically, Gaza obtained its water from a shallow aquifer below its sandy soils. This aquifer was already overexploited before 1967, when Egypt controlled the Gaza Strip, and extensive contamination by seawater occurred. Its annual recharge from rainfall is no more than 1.8 to 1.9 billion cubic feet, but Gaza’s rapidly growing population uses more than 6 billion cubic feet of water a year. This mounting deficit exacerbates the problem: Last year, the United Nations reported that 95 percent of the aquifer’s water was unfit for human consumption because of pollution from seawater intrusion, fertilizers and sewage. Demand is expected to increase by 60 percent by 2020.

Well aware that the water in their taps makes them sick, many Gaza residents purchase bottled and filtered water at considerable cost. Others take matters into their own hands. After the 2005 Israeli withdrawal, thousands of unregistered wells were drilled in Gaza — causing water tables and water quality to decline still further.

Gaza’s water crisis can be tackled, but fundamental change is necessary to begin the slow process of aquifer restoration. Water demand needs to be controlled effectively. A reduction can be achieved by better conservation in domestic supply and in agriculture, while new infrastructure will save on loss through leaks in the municipal system. But technical fixes alone won’t reduce demand as long as Gaza’s population continues to grow at a steep annual rate of 3.2 percent.

A complete moratorium on groundwater extraction is imperative. Gaza’s water should come from alternative sources, such as comprehensive programs to collect roof rainwater and catch runoff from streets. Sewage treatment should be upgraded so that wastewater can be reused in agriculture (as is done in water-stressed states like Texas and Arizona).