RO membranes typically include a waste path so they're self-cleaning for their lifecycle, but some manufacturers may have flushing procedures to extend service life.
Saudi Arabia, Kuwait, UAE, Qatar, Bahrain, and Libya are almost completely dependent on RO for water.
The Carlsbad plant in San Diego was $1B and costs $80M/y (@ 40 MW) to operate while producing 56k acre-ft/y (7% of demand), enough for about 400k people or 20k acres of farmland with average crops.
What would cut water use greatly would be the elimination of meat agriculture which depends on crops such as hay, alfalfa, and cow corn. 2/3 of Utah's water goes to irrigating crops to feed cows.