The Gaza Strip's water provider on Wednesday urged the area's 1.5 million people to boil their drinking water, blaming Israel for a shortage of purifying chlorine. The Coastal Municipality Water Utility made the announcement in radio and newspaper advertisements, telling residents that the sanctions have left Gaza without equipment and supplies needed to maintain the water system. Officials said there have been no deliveries of chlorine, needed to purify the water, since Jan. 21. More than one-third of Gaza's water supply is now untreated, said Maher Najjar, deputy director of the utility. The authority said there is a "major concern over a health disaster due to possible contamination of the drinking water" and appealed to the international community for help. The IDF said the Palestinians did not make a request for chlorine until Wednesday, and it was urgently trying to arrange a new shipment into Gaza. The chlorine shortage is another addition to Gaza's water woes. Most residents don't have regular water supplies because of a shortage of fuel used to pump water. Many people already use filters or bottled water because the quality of tap water is generally poor. Israel imposed sanctions on Gaza after Hamas seized power last June. Israel has tightened its blockade in recent weeks in response to repeated rocket attacks on southern Israel by Gaza terrorists. On Wednesday, an Israeli student was killed in a rocket barrage on a college just outside Gaza, after seven Palestinians, including five Hamas gunmen, were killed in Israeli air strikes. Under the sanctions, Israel, the main gateway for Gaza's imports and exports, has allowed little more than basic humanitarian goods to enter the territory. It also has reduced fuel and electricity supplies to Gaza. Najjar said 52 of 140 wells used to supply water to Gaza residents were out of chlorine. "I expect by the week's end all the wells will run dry of chlorine," he said. The utility needs about 65 tons of chlorine every month, said Nafiz Alia, the utility's chlorine supplier. Alia said the last shipment into Gaza in January contained 30 tons. He said he used reserve stock to make up the rest. "But I ran out of chlorine completely on Monday," Alia said. Shadi Yassin, an Israeli army spokesman, said Israel only received a request from the Palestinians for chlorine on Wednesday. "We are doing our best to allow the chlorine to enter the Gaza Strip as soon as possible," Yassin said. He said "it's a pity" the Palestinians waited so long to notify Israel. It was unclear how long it would take to deliver the chlorine, but Yassin said it was a "top priority." Israel's sanctions have already affected the Gaza water supply. The water wells rely on pumps powered by electricity. About 100 wells don't have diesel fuel, used during frequent power outages, because of Israel's reduced supply of fuel. When the electricity goes out, the water is knocked out as well, Najjar said. Most Gaza residents who can afford to do so filter Gaza's salty, brackish tap water before drinking it. However, that does not kill the bacteria, Najjar said.