A laboratory result is only as good as the sample it was given, and sampling is where most household well testing goes wrong. Bacteria samples are ruined by ordinary handling, metals results depend entirely on how long the water sat in the pipes, and holding times mean a perfect sample can still produce a meaningless number if it arrives late.
Bacteria: sterile technique and speed
The bottle is sterile and often contains a preservative, so do not rinse it, do not touch the inside of the cap or the neck, and fill it to the line rather than to the brim. Take the sample from a tap without an aerator or hose attachment, or remove the aerator first, and run the tap for several minutes so you are sampling the well rather than the fixture. Some laboratories ask you to disinfect the tap outlet. Then get it into a cooler and on its way the same day, because bacteria holding times are short.
Metals: first draw or flushed, and they differ
For lead and copper, which come from the plumbing rather than the source, a first draw sample from a tap that has stood several hours is what represents what a household actually drinks. For iron, manganese and the well's own chemistry, run the tap until the water is cold and steady so you are sampling the aquifer instead of the pipework. Those two samples answer different questions, and using the wrong one is how a household concludes it has no lead problem or that its well carries iron it does not have.
Everything else
Use the bottles supplied and in the order the instructions give, because some contain acid or other preservatives and filling the wrong one loses the analysis. Do not overfill bottles for volatile compounds, which must have no headspace, and do not underfill others. Label each bottle at the tap rather than afterwards. Record which tap, what time, and how long the water had stood, since a laboratory can interpret a result far better when it knows the conditions.
Getting it there and reading it back
Holding times are real: a sample analysed outside them may be rejected or reported with a caveat, so post or courier as instructed and avoid taking samples the day before a weekend unless the laboratory expects them. When the report arrives, look at the detection limit as well as the result, since not detected means below that limit rather than absent. The EPA notes private wells are not federally regulated under the Safe Drinking Water Act, so keeping the reports and watching the trend is the owner's job. Our well testing guide covers panels.
Questions people ask about well testing kit
Should I rinse the sample bottle?
No. Bacteria bottles are sterile and may contain preservative, and rinsing ruins the sample. Fill to the line without touching the neck or cap.
Should I run the tap before sampling?
It depends. Run it for well chemistry so you sample the aquifer; do not run it for lead and copper, which need a first draw sample.
Does it matter how quickly the sample arrives?
Yes. Holding times are short for bacteria in particular, and a sample analysed outside them may be rejected or caveated.
What does not detected mean on a report?
Below the laboratory's detection limit for that method, which is not the same as absent. Read the limit alongside the result.