The arid Arab countries of the Persian Gulf increasingly rely on desalination for their drinking water. It provides 90% or more of the supply for Bahrain, Kuwait and Qatar, and almost as much for Oman. For Saudi Arabia it is 70%, and roughly 40% in the United Arab Emirates.
The Gulf's most productive desalination plants line the coast, within easy reach of Iranian missiles and drones. An American diplomatic cable written in 2008 (published by WikiLeaks) noted that the Jubail Desalination Plant alone then supplied Riyadh with over 90% of its drinking water; if its pipelines or surrounding power infrastructure were hammered, the city would have to be evacuated within a week.
Since 2006 the Gulf states have spent around $53bn to reduce this vulnerability. Saudi Arabia now gets roughly 40% of its desalinated water from smaller, more spread-out facilities. Abu Dhabi and Qatar are building up strategic reserves. The UAE aims to have reserves equivalent to just two days of normal consumption by 2036, which could be stretched to about a month by strict rationing.
During the third Gulf war, both sides threatened civilian water infrastructure—generally considered a war crime. American forces reportedly struck a plant on Iran's Qeshm Island; Iran then hit one in Bahrain. The IRGC said it would target Gulf countries' water facilities in response to any American attack on Iranian power plants. Iran itself relies much less on desalination but is desperately short of water: decades of dam-building and reckless extraction have depleted supplies, and almost a third of Iranians face shortages.
A mushroom cloud has no silver lining.