# Nitrate in Water Treatment: What Actually Works > Reverse osmosis removes nitrate at the tap; ion exchange and distillation also work. Boiling concentrates it. Compare costs and sizing for a 10 mg/L limit. Canonical: https://watertreatmentpro.com/nitrate-in-water-treatment/ Last updated: 2026-11-09 Nitrate in water is treated by reverse osmosis at the point of use, nitrate-selective ion exchange, or distillation. The federal limit is 10 mg/L, and a treatment system is warranted when a test exceeds it. Boiling does not remove nitrate; it concentrates it. ## Why Nitrate Is Different Nitrate is a dissolved ion, and it passes through sediment filters, carbon blocks, and standard softeners without change. Those devices are designed for particles, chlorine, and hardness, not for anions. That is why a household can have soft, clear, good-tasting water that still exceeds the nitrate limit. The test is the only way to know. Nitrate moves easily through soil and into groundwater, which is why private wells in agricultural areas and near septic systems are the common cases. ## Reverse Osmosis RO removes 80 - 95 percent of dissolved solids, including nitrate. An under-sink unit costs $300 - $900 installed and treats drinking and cooking water at one tap. Running costs are $60 - $150 a year in filters, with a membrane every 2 - 3 years at $40 - $120. The system wastes 3 - 4 gallons for every gallon treated. RO is the default residential answer because it is affordable, quiet, and treats the water people actually drink. Whole-house RO at $3,000 - $8,000 is the option when every tap needs treated water. ## Nitrate-Selective Ion Exchange A nitrate-selective resin exchanges nitrate for chloride, and it regenerates with salt. It is used whole-house or at a point of entry. Installed cost runs $1,000 - $2,500, and the resin needs periodic replacement. The advantage is flow: it treats the whole house without a storage tank or a drain line for reject water. The disadvantage is selectivity. The resin prefers sulfate, so high-sulfate water reduces capacity, and the system must be sized for both. ## Distillation Distillation boils water, condenses the steam, and leaves the minerals behind. It removes nitrate and most other dissolved solids. Countertop distillers cost $150 - $500 and produce a few gallons a day. They use significant electricity, and the process is slow. Distillation suits a household that wants one appliance and no drain connection. It does not suit a family that drinks several gallons a day. ## What Does Not Work | Method | Removes nitrate | Notes | |---|---|---| | Sediment filter | No | Particles only | | Carbon filter | No | Chlorine and organics | | Standard softener | No | Cation exchange only | | Boiling | No, concentrates | Water evaporates, nitrate stays | | UV | No | Disinfection only | | Reverse osmosis | Yes | 80 - 95 percent rejection | | Nitrate-selective resin | Yes | Regenerated with salt | | Distillation | Yes | Effective, energy intensive | The boiling point is the one people get wrong. Boiling is the standard emergency disinfection method for bacteria, and it makes nitrate worse. A household that boils water for a nitrate problem is concentrating the contaminant. ## Sizing and Selection 1. Test the water for nitrate, nitrite, sulfate, and bacteria. 2. Confirm the level against the 10 mg/L limit. 3. Decide whether to treat one tap or the whole house. 4. For a single tap, choose an RO sized for daily drinking volume. 5. For whole-house, confirm the flow and the regeneration requirements. 6. Install with a bypass and a sample tap. 7. Retest at the tap after commissioning. A family drinking 2 gallons a day needs a system rated for at least 5 - 10 gallons a day of product water, with a storage tank that covers peak use. ## Costs Over Ten Years An under-sink RO at $600 installed plus $100 a year in filters plus two membranes at $80 each costs $1,760 over ten years. A nitrate-selective whole-house system at $1,800 installed plus $300 a year in salt and resin amortization costs $4,800 over the same period, and it treats every tap. Whole-house RO at $5,000 installed plus $400 a year in service costs $9,000 over ten years, with more maintenance and more water waste. ## Testing After Treatment Test the treated water at the tap, not the raw water. A nitrate result under 10 mg/L confirms the system is working; a result near the raw number means the membrane is spent or the unit is bypassed. Retest annually, and after any membrane or filter change. Nitrate levels in a well can shift with rainfall and seasonal water table changes. Mixing a high-nitrate supply with a low-nitrate source lowers the concentration. A household with a second well, a cistern, or a municipal connection can blend to stay under the limit. The arithmetic is a weighted average. Ten gallons at 20 mg/L blended with ten gallons at 2 mg/L gives 11 mg/L, which is still over the limit. Twenty gallons at 2 mg/L with ten at 20 mg/L gives 8 mg/L. Blending is a calculation, not a guess, and it needs a way to measure the mix. It also needs a reliable low-nitrate source, which most households with a contaminated well do not have. For those households, treatment at the tap is the practical answer. An RO membrane that has degraded still produces water, and the nitrate rejection falls before the flow drops. A test of the product water is the only way to know. A handheld TDS meter is a rough proxy. If the product water reads 10 - 20 percent of the feed TDS, the membrane is working. If it reads 50 percent, the membrane is passing dissolved solids, and nitrate is likely passing too. Test nitrate directly after a membrane change and again at six months. A result that climbs back toward the raw number means the membrane or the prefilter is failing. For the testing side, see [nitrate in water test](https://watertreatmentpro.com/nitrate-in-water-test/). For the well problem, see [nitrate in well water](https://watertreatmentpro.com/nitrate-in-well-water/). For RO costs, see [reverse osmosis system cost](https://watertreatmentpro.com/reverse-osmosis-system-cost/).