When a water test fails, tell the whole community to boil their drinking water at once, increase treatment, retest at several points to confirm and locate the problem, and look for the cause. Lift the boil-water advisory only when two consecutive hydrogen sulfide tests taken 24 hours apart come back negative and the cause has been found and fixed, remembering that a negative test never proves the water is safe.
Part of Community Water Testing
Responding to a water test failure is the set of immediate steps a community takes when a test shows contamination: warn people, make the water safe to drink, confirm and locate the problem, and decide when it is over.
Warn First, Then Find Out
A failed test means the water may be making people ill now. The page sets out the first steps in this order:
- Notify the community. Issue a boil-water advisory immediately.
- Increase treatment. If you are chlorinating, the page’s instruction is to double the dose temporarily. Treat that as a short-term measure: the dose is set by the treatment procedure and judged by the chlorine residual, 0.5 mg/L after 30 minutes and 0.2-0.5 mg/L at the tap (Chlorination).
- Retest. Take new samples at multiple points to confirm the result and to locate the problem.
Then investigate, and finally lift the advisory under a stated condition. The investigation is in Source Investigation, and the first hours are in Immediate Actions.
How To Boil
A rolling boil, with large vigorous bubbles over the whole surface that stirring cannot stop, for 1 minute below 2,000 meters altitude, and for 3 minutes above it (Rolling Boil). Use the boiled water for drinking, cooking, brushing teeth, washing food that is eaten raw, and making food or milk for babies. Cool it in a clean, covered container and keep it covered.
What You Need
- A way to reach every household quickly: a bell, runners, notices at the standpipes
- Fuel and pots for the community’s drinking water
- The test kit for retests, and the log
- A named person with authority to declare and lift the advisory (Water Committee)
Method: The Steps In Order
Step 1: Declare the advisory. Say what is wrong, what to do (boil for the stated time) and who to tell.
Step 2: Increase treatment in line with the written procedure and measure the residual afterwards.
Step 3: Retest at the source, the tank outlet and the affected points.
Step 4: Investigate the source, tank and pipes.
Step 5: Fix the cause before thinking of lifting the advisory.
Step 6: Retest after the fix, and lift the advisory only when two consecutive tests 24 hours apart are negative.
Worked Example: The Earliest Day The Advisory Can End
A vial read at hour 0 shows black, and the advisory starts at hour 0.
- Retest samples taken at hour 0 are read at the 24 hour mark, hour 24.
- A second sample taken 24 hours after the first, at hour 24, is read 24 hours later, at hour 48.
- If both are negative, the earliest the condition can be met is hour 48, two days. If the committee waits for the full 48 hour read of each vial, it is hour 72, three days.
- A tank cleaned and the cause fixed at hour 30 would put the clock back: the tests after the fix are the ones that count.
The two-test rule is a minimum. Two clear vials are consistent with clean water, and also with contamination that comes and goes.
What A Negative Result Does And Does Not License
A negative hydrogen sulfide test shows no sign of faecal bacteria in that vial, from that sample, on that day. It does not cover viruses, parasites or chemicals, it can miss low levels, and a sample is only as good as its collection. Lift the advisory only if the cause has been found and fixed, the chlorine residual is back in range and the turbidity is normal. If the cause was never found, keep testing for longer, and tell people that you do not yet know why it happened.
Common Mistakes
- Waiting for the retest before warning. Warn first.
- Lifting the advisory after one clear test.
- Fixing the water and never finding the cause. It will happen again.
- Telling people to boil but not how long.
- Overdosing chlorine to the point people avoid the tap. They then drink from unsafe sources.
Safety
A boil-water advisory is a safety measure for everyone, so make it reach everyone
Include the vulnerable first: infants, the sick, the old. Boiling must be a full rolling boil for the stated time, and boiled water must be stored in clean covered containers. Do not mix chlorine with acids, vinegar or ammonia products when increasing treatment or disinfecting a tank; entering a tank or well to clean it needs ventilation, a harness on a line held by a person outside, and a rule that the person outside never goes in after a collapsed worker. Do not test the air with a flame.
What’s Next
- Learn next: Immediate Actions — the first hours in detail
- Combine with: Source Investigation — finding the cause