Cadmium
A kidney toxin that usually arrives from corroding galvanised pipe rather than from the ground.
- Safe range
- 0 – 0.005 mg/L (US EPA primary standard, with the health goal set at the same figure.)
- Measured in
- mg/L
What it is
Cadmium reaches drinking water mostly as an impurity in the zinc of galvanised plumbing and in some older solders and fittings, and from industrial discharge or fertiliser run-off where those exist. Natural levels in groundwater are typically very low.
Why it matters
Cadmium accumulates in the kidneys over a lifetime and is cleared very slowly, so the harm is cumulative rather than acute. Because the usual source is corroding plumbing, a detection is often telling you something about your pipes rather than about your aquifer — and the same corrosive water is very likely delivering lead and copper too.
How to measure it
A laboratory, on a first-draw sample if you suspect the plumbing rather than the source.
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.
Included in standard metals panels. Order it alongside lead and copper rather than alone, since the three share a source.
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.
Monitored and published by public systems, though the report describes water leaving the plant rather than water arriving at your galvanised pipe.
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.
- • First draw, after the water has stood at least six hours, if you are testing the plumbing. A flushed sample tests the utility instead, which is a different question.
Further reading: US EPA: National Primary Drinking Water Regulations, the enforceable health-based limits
If it is too low
Nothing to act on.
- • No action needed.
If it is too high
Long-term kidney damage is the concern. A detection also points at galvanised plumbing or corrosive water, both of which are worth following up.
- • Test lead and copper together — the plumbing that gives up cadmium gives up those as well.
- • Flush the tap before drawing drinking water while you investigate.
- • Reverse osmosis handles it at the tap; replacing galvanised pipe deals with the cause.
Common questions
Where does cadmium in tap water come from?
Most often from the zinc coating inside galvanised pipe, which contains cadmium as an impurity and releases it as the pipe corrodes. Industrial discharge and fertiliser run-off are the other routes, but plumbing is the common one in a home.
Does a carbon filter remove cadmium?
No. Activated carbon is for chlorine, taste, odour and organic compounds; dissolved metals pass straight through. Reverse osmosis is the point-of-use option that works.
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.