Crown Prince Muhammad puts desalination at the top of his privatization drive. “In 2019 we will start privatizing more than 20 companies. Most in desalination,” he says. But, as often with his grandiose pronouncements, the devil is in the detail. What will be offered is unclear, whilst the country’s ageing plants need investment.

Saudi Arabia holds the world’s largest national seawater desalination capacity – unsurprising, given the country’s climate and...