Remineralization of reverse osmosis produced drinking water: Impact of magnesium on biological stability and microbial community

Desalination, particularly via reverse osmosis, has become a critical water supply method in waterscarceregions, yet RO-treated water often needs remineralization due to its low hardness and corrosivenature. Our research shows that supplementing magnesium up to 50 mg/L does not adversely impactmicrobial abundance (e.g., total and intact cell counts, ATP) but can enrich potentially beneficial taxaand suppress opportunistic pathogens like Legionella. These results have direct implications for publichealth and for utilities seeking to optimize remineralization protocols while maintaining water qualityand safety.We conducted both hydrostatic and hydrodynamic experiments over an extended period to captureimmediate and long-term effects of different magnesium (and calcium) remineralization on bacterialyield, biofilm growth, and community composition. Our findings highlight the importance of controllingassimilable organic carbon rather than just adjusting magnesium levels to maintain the biologicalstability of RO-produced water.