By ion exchange. The tank holds 2.5 cubic feet of ResinTech SIR-100-HP, a nitrate-selective strong base anion resin in chloride form. As water flows through the bed, the resin swaps harmless chloride ions for nitrate ions and holds the nitrate on the bead. When the metered valve sees you've used enough gallons, it regenerates the bed with a sodium chloride brine (ordinary water softener salt), flushes the captured nitrate to the drain, and restores the resin to chloride form. It's the same mechanic as a water softener, with a resin engineered for nitrate instead of hardness.

Yes. Nitrite is also an anion, and the same resin captures it. The EPA limits are 10 ppm for nitrate and 1 ppm for nitrite, both measured as nitrogen. Nitrite at 1 or more is uncommon: none of the 105 well tests with a nitrite result that my customers got back since August had it. Test for both before and after install so you can see the numbers on a lab report.

The manufacturer rates this system at 10 GPM, and we list it for homes with 3 or more bathrooms. It holds 2.5 cubic feet of resin in a 13 x 54 inch tank. The nitrate filter I recommend most often is our Fleck 5600SXT nitrate filter: 1.5 cubic feet in a 10 x 54 inch tank, at the same $2,895. If your home needs more flow than one unit gives, two units can be plumbed in parallel. Call or text me with your test and your bathroom count, and I'll tell you which one fits.

It uses salt the way a softener does: pellet salt in the brine tank, drawn each time the valve regenerates. The valve counts the gallons you use and regenerates when the programmed amount is reached, not on a clock, so your salt use depends on your nitrate and sulfate levels and how much water your home uses. Plain pellet salt from Walmart, Lowe's or Home Depot runs about $8 for a 40 lb bag. Send me your test and I'll estimate your salt use. On hard water, the softener ahead of it keeps the brine water soft, which ResinTech recommends to keep scale out of the resin.

Sulfate competes with nitrate for capacity on any anion resin. SIR-100-HP is specifically engineered to prefer nitrate, so unlike generic type 1 or type 2 anion resin it will not dump captured nitrate back into your water even after the sulfate break. But high sulfate still reduces working capacity, which changes how the system should be sized and how often it regenerates. If your lab report shows elevated sulfate, call us with the numbers before ordering and we'll confirm the right configuration.

Maybe. This system treats every faucet in the house; an under-sink RO treats one, the kitchen sink. I tell nitrate callers to expect an RO to take out about half, up to 70 percent, depending on water temperature and pressure, so at 20 ppm the RO water can still be at the limit. If you only need drinking and cooking water, the RO treats the kitchen sink for $595; test the RO water after it goes in to see where it lands. With a baby under 6 months in the house, Minnesota's health department recommends bottled water for the baby even with treatment in the house, in case the treatment fails. Send me your test and I'll tell you which fits.

I tell callers the nitrate resin lasts about 10 to 15 years. It regenerates with salt every cycle instead of being used up. When it does wear out, you rebed the tank with replacement SIR-100-HP resin rather than replacing the system. Nitrate showing up again in your treated water is the sign it's time, so test the treated water once a year.

Because softener resin is a cation resin: it removes calcium and magnesium (hardness), which are positively charged. Nitrate is an anion, negatively charged, and passes straight through softener resin. The reverse is also true, which is why the treatment order matters: the softener goes upstream to remove hardness, and the nitrate system goes after it. Removing hardness first protects the nitrate resin and keeps the brine makeup water soft.

Yes. Nitrate has no color, taste or smell, so only a test tells you your level, and to size the system I need a lab test with nitrate, nitrite, sulfate and hardness. Our $199 well water test covers all four; the $139 nitrate test gives the nitrate number only. The EPA says to test a private well for nitrate every year. Or send us the report you already have, and we'll personally confirm the right system before you spend anything.