Israel must immediately ease its Gaza Strip blockade to allow in spare parts and building materials to repair the territory's dilapidated sewage and water networks, a top UN official said Thursday, warning of a growing environmental hazard. Some 13 to 21 million gallons of raw or partially treated waste are being pumped from Gaza into the Mediterranean every day for lack of treatment plants and storage pools, said Maxwell Gaylard, the UN humanitarian coordinator in the Palestinian territories. The waste also threatens neighboring countries, Gaylard said, in a reference to Israel. Israel and Egypt have kept Gaza largely sealed since a violent takeover of the territory by the Islamic militant Hamas in 2007. Since its three-week military offensive against Hamas last winter, Israel has allowed in food and some goods in larger quantities. However, it continues to ban construction materials, such as cement and pipes, arguing that Hamas could use them to build bunkers and rockets. Israel launched the Gaza war in late December to put an end to years of Hamas rocket fire on Israeli border towns. The blockade has halted repairs of Gaza's already overburdened sewage and water networks, and slowed construction of a globally funded, multimillion dollar waste water treatment plant for northern Gaza. During the war, water and sewage pipes suffered more damage. Gaylard said some 10,000 Gazans don't have access to a water network, and that some 60 percent of a population of 1.4 million receive water only intermittently. Gaylard, other UN officials and representatives of international aid groups were to hold a news conference later Thursday near sewage lagoons in northern Gaza to highlight the problem. One of the lagoons overflowed in 2007, killing five people. "The deterioration and breakdown of water and sanitation facilities in Gaza is compounding an already severe and protracted denial of human dignity in the Gaza Strip," Gaylard said.