This may explain a bit.
http://www.nyjtimes.com/cover/05-06-...raeliWater.htm
"[w]hen Gaza was turned over to the sole ruling authority of Arafat's PA, it received total control of the Gaza aquifer - which at the time was still functioning and producing potable water. Within less than two years under Palestinian Arab management, the Gaza Aquifer was ruined, contaminated beyond repair. If the PA is incapable of taking care of its own aquifer to supply water to its residents, how can Israel place its trust in the same Authority to care and conserve water sources that supply Israeli taps?"
The Coastal Aquifer extends south to include all of the Gaza strip as well as the site in the Sinai where once Israelis built Yamit. Abandonning the coastal tail of the aquifer to the Egyptians - thus reducing Israel's water supply - compounded the damage to the aquifer by present-day overutilization. The remains of Yamit are a memorial - and a warning - of the first expulsion of Jews by Jews.
Atlas also points out the consequences of Israel's allowing the Mountain aquifer to fall into Arab hands:
[Given what has happened to the Coastal aquifer] "the importance of the Mountain Aquifer has increased. As Israel's State Comptroller's Annual Report already reported by the early 1990's:
"The Mountain Aquifer, extending eastward of the Coastal Aquifer, from the slopes of Mt. Carmel to Beersheba, and from the crests of mountain ridges in Judea and Samaria to the coastal plain, serves as the principle reservoir of drinking water to the Dan region, Tel Aviv, Jerusalem and Beersheba. Today, it is the most important long term source in the [National] Water System."
"Now comes the political problem. This 'most important long-term source' physically straddles the pre-1967 cease fire lines, alias 'the Green Line', into Judea and Samaria. The Principle of Connecting Vessels tells us that any activity affecting the water on one side will affect that on the other side as well. So if pumping operations, or uncontrolled flow of sewage or industrial waste, etc., occur on the western slopes of Judea and Samaria, it would cause serious, and most probably irreversible, damage to the key source of drinking water for Israel's major urban centers and environs.
"The political and strategic significance for Israel is clear. Withdrawing from Judea and Samaria - i.e., the Mountain Aquifer - or from the Golan Heights would create a situation in which the fate of Israel's water supply would be determined by Mr. Arafat's Palestinian Authority and the Syrians, respectively. [underscoring added]
"Can Israel really afford to trust her most valuable and irreplaceable national resource in the hands of those who have had a long history of trying to destroy the Jewish State? In the case of the Syrians, this includes diverting and/or poisoning Israel's water supply."
Whether through malevolence, ignorance or seeing the Middle East through Arab-colored glasses, much of the press presents a distorted picture of water usage between Israel and the Palestinian Arabs, wherein Israel is the villain. In the summer of 1998, as an example, the New York Times compared how the West Bank Arabs were "parched" for drinking water while the Jewish settlers near Hebron watered lawns and washed cars.[9] The Times knew exactly how incendiary the story was - accuracy wasn't its objective. The facts were much different - the settlers needed to drink bottled water because they didn't have drinkable water while the Arabs don't distribute their water equitably but sell their water privately or steal it and then sell it.
What goes unreported is the extent to which Israel shares water with her neighbors. Camera[10] pointed out in 2002 that
"... every year over 40 MCM (million cubic meters) of water from sources within Israel is piped over the Green Line for Palestinian use in the West Bank. Ramallah, for example, receives over 5 MCM. Israel sends another 4 MCM over its border for Palestinian use in Gaza. Thus, it is the Palestinians who are using Israeli water.
"And not just the Palestinians. Despite its own meager supply, Israel annually provided 600,000 CM of water to ten otherwise dry villages in South Lebanon, and provides more than 55 MCM annually to Jordan."
"In addition, Israel also supplies more than 4 MCM annually to the Gaza Strip through the Kissufim Line of the National Water Carrier, serving the Palestinian localities of El-Bureij, Moazi, Abasan, Bani Suheila and Khan Yunis" (Statistical Data on Gaza Area and Jericho, Israel Foreign Ministry, June 1994).