Keep a water test log at a central place and record, for every test, the date and time, the location, the test, the result, the weather and the action taken, adding who tested, the batch of test medium and whether the blank and positive controls were right. Review it monthly for trends, because a turbidity reading that falls from 42 to 30 centimeters over 5 weeks is invisible in any single reading and obvious in a list.
Part of Community Water Testing
A test log is the written record of every water test, kept so that results can be compared over time, shown as proof of safety checks, and used to spot slow declines before they become a crisis.
A Log That Is Not Reviewed Is Paper, And A Log That Is Not Kept Leaves You Guessing
The community water testing page asks for a simple logbook kept at a central location and a monthly review for trends, listing six fields for each test. The reasons it gives: without written records you cannot spot trends and cannot prove the water was safe.
The six fields are: date and time; location (source, tank, standpipe number); test performed (turbidity, H2S, pH, visual); result (a measurement or pass/fail); weather (recent rainfall, temperature); and action taken, if any. Add these so that results can be trusted later:
- Who tested, so questions can be asked
- Batch and date of the H2S medium, and the blank and positive control results for that batch
- Incubation start and read times, and the temperature
- Time since the last chlorine dose for residual readings
- Sample volume for bacteria tests
What You Need
- A bound book with numbered pages, or a sheet in a binder, and a pencil or pen that does not run
- A copy kept elsewhere, because a flood or a fire takes the original
- A standing monthly review on the calendar
Method: Write It Down At The Time, Fix Nothing In Secret
Step 1: Write the entry at the point of testing, not that evening from memory.
Step 2: Record failures and ordinary results alike. The good readings define the normal.
Step 3: Never erase. Strike out a wrong entry with one line, initial it and write the correction beside it.
Step 4: Record the action, even if the action is “none, routine”.
Step 5: Review monthly. Plot or list readings by point over time. Look for drift, steps and a change after an event.
Step 6: Make a second copy each season and store it in a different place.
Worked Example: A Slow Decline
Weekly tube readings at the spring: 42, 40, 38, 35, 33 and 30 cm over weeks 1 to 6.
- Change from week 1 to week 6: 42 - 30 = 12 cm over 5 intervals.
- Rate: 12 ÷ 5 = 2.4 cm per week.
- Every single reading but the last is above 30 cm, the “good” line, so no test failed.
- If the rate continues, week 7 would read about 30 - 2.4 = 27.6 cm and week 8 about 25.2 cm, both in the marginal band.
Without the log the first sign of trouble would be the first marginal reading in week 7. With it, the decline is visible from week 3, and the cause (a catchment being cleared, a damaged diversion ditch, a season change) can be sought before the water leaves the good band.
Similarly, count positives: a spring with no black vial in 11 months and two in the 12th says something has changed in the last month, and the log shows when.
Sample Page Layout
| Date, time | Place | Test | Result | Weather | By | Action |
|---|---|---|---|---|---|---|
| 3 Mar 08:10 | Spring box | Tube | 35 cm | Dry 3 days | A.K. | None |
| 3 Mar 08:40 | Tank outlet | H2S, batch 4 | Set up with blank and positive control; read at 24 h and 48 h | Dry | A.K. | Reads due next two days |
Common Mistakes
- Writing it up from memory.
- Recording only failures.
- Erasing a wrong entry. Strike through and correct.
- Keeping one copy.
- Never reviewing. The log then stores data and warns nobody.
Safety
A record is evidence, and it can mislead
A log full of clear results looks reassuring, but each entry describes one sample at one moment. Do not read a run of clear results as proof of safety: bacteria tests can miss low-level contamination, they do not cover viruses, parasites or chemicals, and a clear result the day before an outbreak is normal. The log supports decisions; it does not replace the daily look.
What’s Next
- Learn next: Responding to Failures — what a bad entry should trigger
- Combine with: Decision Archives — keeping records that outlast the people who made them