Nitrates in Well Water: Test, Treat, Re-Test

Signs of nitrate

There aren’t any you can see, taste or smell. A lab result is the only sign. The State Water Board recommends that domestic well owners sample at least annually through a state-accredited lab [State Water Board: Nitrate in groundwater FAQ], and the CDC says all well owners should test for nitrate at least once every year [CDC: Guidelines for testing well water].

The limit, and the Valley picture

California’s drinking water limit is 10 mg/L for nitrate measured as nitrogen, the same as 45 mg/L measured as nitrate. Check which unit your lab report uses [State Water Board: Nitrate in groundwater FAQ]. Private wells aren’t regulated by the state, but the MCLs can be used as guidance [State Water Board: Nitrates and nitrites in drinking water]. Nitrate is regulated for health reasons, and the CDC notes that high levels can make people sick, especially babies [CDC: Guidelines for testing well water]. For health questions, talk with your doctor or county environmental health.

The USGS reported nitrate above the 10 mg/L limit in 24% of shallow domestic wells sampled in the eastern San Joaquin Valley in 1993–95 [USGS: Nitrate trends in the eastern San Joaquin Valley]. In the Modesto, Turlock and Merced groundwater subbasins, moderate and high nitrate turned up only in the upper 200 feet of the aquifer system [USGS Fact Sheet 2010-3001: Groundwater quality, Central Eastside San Joaquin Valley], the depth many private wells draw from.

City systems watch it closely too. Turlock’s 2025 report shows groundwater nitrate averaging 5.58 ppm (parts per million), with a high of 9.84 ppm against the 10 ppm limit [City of Turlock 2025 Water Quality Report], and Hilmar County Water District’s 2024 report lists a nitrate MCL (maximum contaminant level, the legal limit for public drinking water) violation [Hilmar County Water District 2024 Consumer Confidence Report]. See Turlock water.

How we test for nitrate

1. Free in-home water test. We come to you and check the basics at your tap: hardness, precipitation, chlorine and soap testing, and more, depending on what you’re noticing.
2. Lab test where it matters. For anything with a health-based limit, we arrange a state-certified lab test and walk you through the report in plain English.
3. A written, no-pressure estimate for only what your water calls for. Sometimes that’s nothing at all.
4. Tested before, tested after. Once your system is in, we test again, with a follow-up lab test for health-related contaminants. If the results don’t match what we showed you, we adjust it at no charge.

How we treat it

For nitrate, whole-house anion exchange is our primary and most effective method. It reduces nitrate for every tap in the house, so drinking, cooking, ice and showers are all covered. We size it from your lab results and household water use, and we arrange another lab test after install so you can see the reduction on paper.

Reverse osmosis can also reduce nitrate, though less effectively than anion exchange. It’s typically an under-sink option for drinking and cooking water at the kitchen sink, and some families add it as an extra layer. See reverse osmosis.

What treatment gives you

• Confidence in every glass, with a lab result after install to prove it.
• A protected family, with treated water at every faucet, not just one.
• No more hauling bottled water for drinking, cooking and baby formula.
• A plan for the future, with annual testing reminders and service from the same team.

How whole-house anion exchange works

Anion exchange uses a special resin that trades nitrate in your water for chloride as water flows through the tank. When the resin is loaded, the system regenerates itself on a schedule we set from your test results and water use. Because it sits where water enters the house, every faucet, shower and appliance gets treated water.

When to re-test

Nitrate levels can change with the seasons, rainfall, irrigation and what happens on nearby land. Beyond the yearly test, the CDC recommends testing again if there’s flooding or land disturbance near your well, if any part of the well system is repaired or replaced, if your water’s taste, color or smell changes, or if someone in the home becomes pregnant or a child starts living with you [CDC: Guidelines for testing well water]. We’ll remind you, and we’ll test after install so you have a baseline.

Nitrate testing near you

We help well owners across the corridor: Manteca · Lathrop · Stockton · Patterson · Hughson · Turlock · Modesto.