Under Israeli siege, most Gazans lack access to clean water that is crucial for survival.
Israeli fighter jets struck the southern part of the Gaza Strip in an overnight raid on Sunday, targeting what the Israeli military said was an arms smuggling tunnel.
The aircraft attacked a tunnel on the Rafah sector on the border with Egypt, but no one was injured, witnesses said on Monday.
An Israeli military spokesman confirmed that raid, saying it had come in response to nine rockets fired into Israel from the Gaza Strip since Thursday, which left one Thai worker dead.
The raids on the Gaza Strip come in the wake of a visit by Ban Ki-moon, the UN secretary-general, to the Hamas-controlled territory.
Ban condemned the Israeli blockade of the territory, which he said had caused “unacceptable suffering”.
The blockade has been imposed for about three years and, because it denies Gazans access to many goods, the so-called tunnel economy has thrived as Gazans seek to bring in materials from outside the strip.
The raids also follow a series of deaths in the occupied West Bank.
Two Palestinians were shot dead by Israeli troops near an army checkpoint close to the town of Nablus on Sunday.
Another two Palestinians died after apparently being shot by Israeli troops during violent protests in the city itself.
Medical workers say the dead were hit by live ammunition and an X-ray of one of the boys showed what appeared to be a bullet lodged in his head.
Israel has denied its troops used live ammunition and says it has launched an investigation.
Late on Monday, Israeli troops and Palestinian fighters exchanged gunfire near the Kissufim crossing point into the Gaza Strip, Israel’s Channel 10 television reported.
And in a separate incident an Israeli soldier was killed in a “friendly fire” incident near the border with Gaza, an army spokesman said.
The military said two groups of soldiers were tracking three Palestinian suspects who had crossed the security fence to the Israeli side when one group mistook the other soldiers for the Palestinians and fired.
The three Palestinians, who were not armed, were arrested.
Palestinians from the blockaded territory have been known to cross the fortified border in the same area in search of work in Israel.