Community Water Testing

Why This Matters

Clean-looking water kills people. You cannot see bacteria, viruses, or most chemical contaminants. Without testing, you’re guessing — and a wrong guess means dysentery, typhoid, or worse spreading through your entire community. Simple tests done regularly are your early warning system.

Turbidity: The First Check

Turbidity measures how cloudy the water is. It’s not a complete safety test, but it’s the fastest indicator that something has changed.

Building a turbidity tube:

1. Take a clear plastic or glass tube, 50-60cm long, 3-4cm diameter (a clear water bottle with the bottom cut off works)
2. Draw a thick black cross or circle on white paper
3. Place the paper under the tube and look down from the top
4. Fill the tube with water until you can no longer see the mark

The depth at which the mark disappears indicates turbidity:

• >30cm: Good — low turbidity
• 10-30cm: Marginal — investigate the cause
• <10cm: Bad — do not distribute without treatment

Test turbidity at the source, after treatment, and at distribution points. If turbidity suddenly increases at the source after rain, your source protection is inadequate.

Biological Testing: The H2S Test

The hydrogen sulfide (H2S) presence/absence test detects fecal contamination. It’s the most important field test you can do.

Making H2S test medium:

• Mix: 20g peptone + 10g ferric ammonium citrate + 5g sodium thiosulfate + 1 liter of water
• Alternatively, use a simplified version: dissolve rusty iron nails in vinegar for 2 weeks, mix with gelatin and water
• Sterilize by boiling for 20 minutes
• Pour 10ml into small, clean, sealable containers (glass vials or sterile plastic bags)

Using the test:

1. Add 20ml of your water sample to the container with the test medium
2. Seal it and place in a warm location (25-35 degrees C) for 24-48 hours
3. If the water turns black, fecal bacteria are present — the water is contaminated
4. If it stays clear or yellow, the test is negative — water is likely safe from fecal contamination

Warning

A negative H2S test does not guarantee water is safe — it only indicates the absence of one type of contamination. It does not detect viruses, parasites, or chemical contaminants.

Visual and Sensory Indicators

Trained observation catches a lot:

Observation	Possible Cause	Action
Green tint or slime	Algae growth	Clean tank, block light, increase circulation
Reddish-brown color	Iron or rust	Check for corroding pipes, may need iron removal
Rotten egg smell	Hydrogen sulfide (anaerobic bacteria)	Serious — flush system, investigate source
Chlorine smell	Residual from treatment	Normal if chlorinating; test residual level
Oily film on surface	Petroleum contamination or natural minerals	Investigate source — petroleum is dangerous
Tiny worms or larvae	Mosquito breeding, biofilm	Clean tank, repair screens, check for openings

pH Testing with Natural Indicators

Safe drinking water should have a pH between 6.5 and 8.5.

Red cabbage indicator:

1. Chop red cabbage finely and boil in water for 15 minutes
2. Strain — the purple liquid is your indicator
3. Add a few drops to your water sample
4. Red/pink = acidic (pH <6), purple = neutral (pH 6.5-7.5), green = alkaline (pH 8+), yellow = very alkaline (pH 10+)

Turmeric indicator: Soak turmeric powder in water to make a yellow solution. Dip paper strips in it and dry. These strips turn reddish-brown in alkaline water (pH >8).

These won’t give precise numbers, but they’ll tell you if your water is dangerously acidic or alkaline.

Monitoring Schedule

Routine testing:

• Daily: Visual check at source and tanks (color, smell, turbidity by eye)
• Weekly: Turbidity tube measurement at source and distribution points
• Monthly: H2S test at source, tank outlet, and 2-3 distribution points
• After treatment changes: Test within 24 hours of changing chlorine dose, switching filters, etc.

Test immediately after:

• Heavy rainfall or flooding
• Illness outbreak in the community (especially diarrhea)
• Any repair work on the system
• Dead animal found near the source
• Visible change in water color, smell, or taste
• Earthquake or landslide near the source

Record Keeping

Keep a simple logbook at a central location. For each test, record:

1. Date and time
2. Location (source, tank, standpipe #, etc.)
3. Test performed (turbidity, H2S, pH, visual)
4. Result (measurement or pass/fail)
5. Weather (recent rainfall, temperature)
6. Action taken (if any)

Review the log monthly. Look for trends: is turbidity gradually increasing? Are H2S failures becoming more frequent? Catching a slow decline early prevents a crisis.

When Tests Fail

Immediate steps:

1. Notify the community — issue a boil-water advisory immediately
2. Increase treatment — if chlorinating, double the dose temporarily
3. Retest — take new samples at multiple points to confirm and locate the problem

Investigation:

• Walk the entire system from source to taps, looking for obvious contamination points
• Check for animal access to the source, broken spring box seals, cracked pipe joints
• Check uphill of the source for new latrines, animal pens, or disturbed soil
• Test at progressively closer points to the source to isolate where contamination enters

Lift the advisory only when two consecutive H2S tests (taken 24 hours apart) come back negative.

Common Mistakes

Mistake	Consequence	Prevention
Testing only at the source	Misses contamination in tanks or pipes	Test at source, tank, and distribution points
Testing only when there’s a problem	Misses gradual deterioration	Stick to the routine schedule
No written records	Can’t spot trends, can’t prove safety	Keep the logbook, review monthly
Declaring water safe based on one good test	Contamination is intermittent	Multiple tests over time build confidence
Ignoring visual/smell changes	These are early warnings	Investigate any change, even subtle ones

What’s Next

• Water Treatment at Scale — treating water that fails testing
• Community Water System — the system you’re testing
• Water Purification — individual-level backup when the system fails