How Much Nitrate Do Home RO Units Remove?
A standard rejection rate chart for thinfilm RO membranes that we use gives the rejection rate for nitrates as 93% to 96%. Other charts we’ve seen put the rate as low as 80%. While nitrate is removed handily by small RO units, it isn’t what RO is best at.
Factors that affect performance negatively are low water pressure, low pH, and high sodium and sulfate levels.
If water pressure is low, adding a pressure boosting pump to the RO unit would enhance performance. Or, if very low nitrate levels are essential, you can add a nitrate-specific anion cartridge to your undersink RO unit which should assure virtual 100% nitrate reduction. A small nitrate cartridge operating as an RO post-filter will normally have more than enough capacity for a year of service between cartridge changes.
Nitrates are mainly a drinking water issue, so whole house treatment is usually unnecessary.