Nitrite (as N)
Nitrate's short-lived cousin, with a much tighter limit and the same danger to infants.
- Safe range
- 0 – 1 mg/L (US EPA primary standard, expressed AS NITROGEN. Laboratories also report nitrite as the ion, which is a substantially larger number for the same water — check which convention your report uses.)
- Measured in
- mg/L
What it is
Nitrite is an intermediate stage in the nitrogen cycle, sitting between ammonia and nitrate. It is unstable in oxygenated water and usually converts onward to nitrate quickly, which is why it is normally found at much lower levels — and why finding it at all suggests something recent and nearby.
Why it matters
Nitrite causes the same harm as nitrate — methaemoglobinaemia, or blue baby syndrome, in which the blood loses its ability to carry oxygen — but it does so far more efficiently, which is why its limit is an order of magnitude tighter. A meaningful nitrite reading is also a red flag in its own right: because it does not persist, it points at active contamination close by, such as a failing septic system, rather than at the slow agricultural build-up that produces nitrate.
How to measure it
Strips will tell you whether it is there, which is most of the question, because normal is essentially none. A laboratory gives you the number and should be involved if a strip says anything at all.
Test strips
- How trustworthy
- Dependable
- Cost
- Low cost
- Effort
- Under a minute, wherever you drew the sample
A plastic strip with reagent pads on it. Dip it, hold it level, and match each pad against the chart on the bottle at the time the label tells you to. Most strips read several parameters at once.
Nitrate/nitrite strips have two pads and read both at once. As a screen for something that should be absent, this is a genuinely useful home test.
Watch out: The nitrite pad develops faster than the nitrate one. Read each at its own stated time rather than both at whichever you remember.
Where to find it: Pool shops, hardware stores, supermarkets and online, sold both per parameter and as multi-packs. Buy strips made for your kind of water: pool strips and drinking water strips read very different scales for the same chemistry.
Certified laboratory, mail-in kit
- How trustworthy
- Reference grade
- Cost
- Most expensive
- Effort
- Careful sampling, then days or weeks of waiting
You are posted bottles and instructions, you fill them exactly as told, and you post them back. Weeks later a report arrives with figures nobody has to interpret by eye. This is what a result you intend to act on should be built from.
Part of every basic well panel, alongside nitrate and coliform. That grouping exists because the three interpret each other.
Where to find it: State-certified drinking water laboratories; your state's certification officer keeps the list, and many public health departments will point you at one.
Your utility's annual water quality report
- How trustworthy
- Reference grade
- Cost
- Free
- Effort
- A few minutes of reading
Every community water system in the US has to publish one each year, free, listing what it found and what the limits are. It is real laboratory data about the water leaving the plant and travelling the mains. What it cannot describe is your own plumbing.
Regulated and published annually. Detections on a treated public supply are rare.
Where to find it: Your water bill, your supplier's website, or the EPA's index of reports. It is also called a Consumer Confidence Report or CCR.
Taking the sample
For several of these the sample is where the error is, and no instrument recovers from a bad one.
- • Nitrite converts to nitrate in the bottle, so a sample that sits reads low and the nitrate reads high. Use the laboratory's preserved container and post it the same day.
- • Sample from a tap that has been run for a minute, so you are testing the well rather than water that has been standing in the pipe.
Further reading: US EPA: National Primary Drinking Water Regulations, the enforceable health-based limits; US EPA: private drinking water wells, including what to test for and when
If it is too low
Nothing to act on. This is where nitrite normally sits.
- • No action needed.
If it is too high
Do not give the water to infants under six months or use it to make formula. It also indicates active, nearby contamination, which needs finding.
- • Do not use it for infant formula. Boiling makes this worse, not better, because it concentrates it.
- • Test for bacteria immediately. Nitrite and coliform together strongly suggest sewage or septic influence.
- • Inspect septic systems, well seals and any animal housing uphill of the well.
- • Reverse osmosis, ion exchange and distillation remove it; carbon filters do not.
Common questions
What is the difference between nitrate and nitrite?
They are two oxidation states of the same nitrogen. Nitrite is the less stable one and normally converts to nitrate quickly, so it is usually found at far lower levels — but it causes the same infant health effect much more readily, which is why its limit is far tighter.
Why does finding nitrite matter more than the number itself?
Because it does not last. Nitrate can accumulate slowly over years from fertiliser use, but nitrite converts away, so measurable nitrite implies a source that is active and close — a failing septic system being the classic example. That is worth investigating regardless of whether the reading is over the limit.
WiseWaterGauge helps you record and understand your own readings. It is not a substitute for a certified laboratory test, and nothing here is medical or regulatory advice. If a health parameter is out of range, confirm it with an accredited lab and speak to your water provider.