How to Test Well Water: Taking a Sample the Lab Will Accept

Before you start

• Get the bottle from the lab. Bacteria bottles are sterile and contain a preservative^1,2. Québec, British Columbia and Health Canada all tell you to follow the lab’s instructions^3,4.
• Check the time limit and drop-off hours. Public Health Ontario asks you to confirm how soon the sample must be submitted so it is tested within 48 hours¹. Iowa’s lab says to avoid mailing on a Friday, a weekend or before a holiday².
• Sample early in the week, early in the day, so the bottle reaches the lab in time.

Bacteria sample: the steps

Public Health Ontario’s instructions for private wells¹, with what other labs add:

1. Choose an indoor cold-water tap. The kitchen tap, with the aerator, screen or attachment removed. If you can’t remove it, use another indoor tap without one, such as the bathtub. Never an outside faucet or a garden hose¹. Iowa’s lab adds: no sprayer or swivel faucet, and no leaking faucet².
2. Run the cold water for 2 to 3 minutes to clear the water that sat in the pipes¹.
3. Clean the spout with diluted bleach (1 part household bleach to 10 parts water) or an alcohol pad. Do not use a flame: it can damage the faucet¹.
4. Run the cold water another 2 to 3 minutes¹.
5. Open the bottle without touching the inside of the bottle or lid, and don’t set the lid down. Don’t rinse the bottle: the preservative inside neutralizes chlorine^1,2.
6. Fill to the line. Too little, and there isn’t enough to test; too much, and the sample can’t be mixed¹.
7. Close it, keep it cool, and take it to the drop-off within the time limit¹. Alberta asks for a cooler with ice packs⁵.

Where the instructions differ

Sampling for bacteria · how instructions differ

Step	What labs say
Clean the spout	Diluted bleach or alcohol, no flame (Ontario)1; flame or bleach only for an outside tap (Iowa)2; no cleaning step (Penn State’s lab)6
Run the water	2 to 3 minutes, twice (Ontario)1; 2 to 3 minutes, or 10 to 15 for an outside tap (Iowa)2; about 5 minutes (Penn State’s lab)6
Before or after treatment	Bacteria after any treatment, chemicals before (Alberta)5
Time limit	24 hours (Alberta)5; 30 hours (Penn State’s lab)6; 48 hours (Ontario, Iowa)1,2

Lead and copper: the first-draw sample

Lead comes from the plumbing, so the test is built the other way around. The US EPA’s homeowner instructions: use a cold kitchen or bathroom tap that has not been used for at least 6 hours, fill a 1-litre bottle with the very first water, and do not remove the aerator⁷. Penn State’s lab also says the water must sit at least six hours and not be run before sampling⁶. Don’t sample from a tap that goes through a softener or carbon filter⁷.

Chemistry samples

For iron, manganese, hardness and similar tests, follow the lab’s bottle and instructions; they often differ from the bacteria bottle. Alberta Health Services takes chemistry samples before any treatment, so the result shows what is in the well⁵. If you are testing whether a filter works, take one sample before it and one after.

After the results

Our test kits guide explains what the main results mean, and our coliform guide covers what to do if bacteria show up. A single result only describes the water on the day you sampled it, so keep testing on schedule.