Over the next few decades, over-use of groundwater is likely to place increasing pressure on the agricultural sector in the Kingdom of Saudi Arabia. This will necessitate increasing application of brackish water desalination, with associated challenges in maintaining water quality and in brine disposal. While continuing technical advances have secured low-cost water for domestic and industrial use, a different set of challenges are arising due to the shift from thermal desalination to reverse osmosis as the principal desalination method. The higher total dissolved solids content in water produced by reverse osmosis presents quality challenges related to corrosivity, disinfection by-products, and boron. These can all be addressed, but in many cases significant additional expenditure will be required. In this report we consider potential future water quality issues through the light of the results of an extensive water quality assessment carried out across the Kingdom of Saudi Arabia in 2020–2022.