European Parliament President Martin Schulz’s speech to the Knesset on Wednesday left some MKs from the right-wing Jewish Home party so livid that they walked out as he spoke.

Mr Schulz had been discussing encounters with young Palestinians the previous day and reported that they want to “live freely in their own country, with no threat of violence, with no restrictions on their freedom of movement”.

He then said: “One of the questions these young people asked me which I found most moving — although I could not check the exact figures — was this: how can it be that an Israeli is allowed to use 70 litres of water per day, but a Palestinian only 17?”

This comment sparked the walkout. It also prompted Prime Minister Benjamin Netanyahu to criticise Mr Schulz for presenting unchecked numbers.

Mr Schulz’s figures do appear to be inflated, but more problematic was the way he framed the issue. He implied that this is a simple matter of Israelis pouring misery on Palestinians and ignored the complexity of water supply.

Palestinians do consume less water than Israelis. How much less is unclear, because computing the figures from the West Bank is a complicated business and, more importantly, because Israel and the Palestinians do not agree on how many Palestinians there are.

The Palestinian quoted by Mr Schulz is almost certainly wrong. Figures discussed by the Israel Water Authority indicate that Israelis use far less than double what Palestinians use.

Both Israel and the Palestinians should take part of the blame for the water gap. But there is a third cause: the Oslo peace process. Oslo set how much water the Palestinians should have access to, and Israel has not stopped them from accessing this quota. But because Oslo was meant to be a short-term arrangement, it did not make provision for population growth. A final-status peace deal would solve this problem.

On occasions, Israel has hampered Palestinian drilling, but more significant is the fact the Eastern Aquifer turned out to be less plentiful than expected at Oslo, causing both Israel and the Palestinians to scale down drilling there. The Palestinians have met some of the shortfall with the help of Israel, which sells it processed water via the Mekorot water company.

In the PA, water theft and faulty piping are serious problems. According to the Palestinian Water Authority’s figures for 2008, in some areas almost 40 per cent of water was lost or stolen.

Israeli approval is needed for many aspects of Palestinian water development, and Ramallah can find Jerusalem less than supportive. But there is much that the PA could do — which it does not do — to improve water infrastructure without Israeli approval, especially in Area A of the West Bank where it has full control. According to a 2008 calculation by the Palestinian Water Authority, one in five residents of Area A cities Jenin and Nablus were not connected to running water.

These figures underscore the complicated nature of water distribution in the West Bank, and why, carefully considered, it is a poor political football.