RIYADH - Saudi Arabia plans to build nine desalination plants for more than 2 billion riyals ($530 million) on the Red Sea coast, its environment minister said on Sunday.The plants will have capacity of 240,000 cubic meters of water per day and will be completed in less than 18 months, Abdulrahman al-Fadhli wrote in a Twitter post.The project, which the minister said was ordered by King Salman in a royal decree, will help government-owned Saudi Saline Water Conversion Corp (SWCC) raise production efficiency and cut operating and capital costs, Fadhli added.He gave no details on funding.