While 100,000 people had their water supply restored on Sunday, 400,000 still had no water, he said.
Separately, the Palestinian Central Bureau of Statistics estimated that the overall physical damage so far amounted to about $1.9bn (£1.4bn).
The UN has asked Israel to open Gaza's borders to allow in construction materials, but so far only basic humanitarian supplies have been let in.
Meanwhile, Arab foreign ministers meeting in Kuwait have failed to issue a statement on the Gaza situation because they disagreed over who was to blame for the conflict.
Egypt said Hamas had invited the attacks, while Syria said Israel should be declared a terrorist entity.
Palestinian medical sources say at least 1,300 Palestinians were killed, nearly a third of them children, and 5,500 injured during the conflict. Thirteen Israelis, including three civilians, were killed.
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