Smell and taste are early-warning senses for a water supply: a rotten-egg smell means hydrogen sulfide from anaerobic bacteria and calls for flushing and investigation, an oily film or fuel smell means petroleum and the water must not be used, and a metallic taste or reddish-brown colour points to iron or corroding pipe. Sniff suspect water, never drink it to test it, and remember that the most dangerous germs have no smell at all.
Part of Community Water Testing
Smell and taste testing is the use of the senses to notice that a water supply has changed, matching an odour or flavour to its likely cause so that the right check or repair follows.
The Nose Finds Changes, Not Safety
Most disease-causing germs give water no smell or taste, so a clean-smelling supply can still be unsafe. The senses are useful for a different job: noticing that something has changed, and pointing at the cause. The community water testing page gives a table for what to do:
| Observation | Possible cause | Action |
|---|---|---|
| Rotten-egg smell | Hydrogen sulfide (anaerobic bacteria) | Serious: flush the system and investigate the source |
| Chlorine smell | Residual from treatment | Normal if chlorinating; test the residual level |
| Oily film on the surface | Petroleum contamination or natural minerals | Investigate the source; petroleum is dangerous |
| Reddish-brown colour | Iron or rust | Check for corroding pipes; may need iron removal |
Other odours and flavours, with the likely meaning and what to do:
- Earthy or musty. A slight earthy smell from a slow sand filter is described on Sand Filters as geosmin, normal and harmless there. A strong earthy or mouldy smell from a tank may mean algae or decay in the tank.
- Metallic taste. Iron, or corroding metal pipe or fittings (Hardness and Iron).
- Salty or brackish. Dissolved salts, perhaps from the source or from a leak of salt water into it.
- Fuel, solvent or chemical smell. Treat it as petroleum or chemical contamination. Stop using the water.
- Strong bleach smell. Too much chlorine, or water that was dosed and not mixed. It is a taste problem and may drive people to untreated sources.
What You Need
- A clean glass or jar, used only for this
- A log of what was smelled, where and when
- A second person to confirm, because noses differ and tire
Method: Sniff, Compare, Record
Step 1: Fill the clean glass about half full from the source, then from a tank outlet and a tap.
Step 2: Sniff, do not drink. Compare the three. If a smell is there at the source and not at the tap, treatment is working on it; if at one tap and not at the others, look at that branch.
Step 3: Ask a second person, separately, without telling them what you smelled.
Step 4: Record it and follow the table.
Step 5: Test. A smell is a reason to run a residual and bacteria test.
Why Smell Cannot Measure The Chlorine Residual
Several pages in this wiki say that treated water should have a faint chlorine smell, and the carrier’s table says to test the residual level. People differ greatly in what they can smell, and noses tire. Use the smell as a hint that chlorine is present and then measure it with a test kit (Chlorine Residual). A faint smell does not tell you that the residual is 0.5 mg/L, and no smell does not prove there is none.
Hydrogen Sulfide Needs Respect
The rotten-egg smell is hydrogen sulfide. In a closed space such as a tank, a well shaft or a pit, it can reach levels that are poisonous. At high levels it dulls the sense of smell, so a smell that fades is not a sign the gas is gone. Do not rely on your nose to decide a confined space is safe. Do not use a flame to check the air.
Common Mistakes
- Tasting suspect water. Sniff it.
- Treating “no smell” as safe. Germs do not smell.
- Using the nose to measure chlorine.
- Ignoring a faint change. Write it down; a trend shows.
- Ignoring a smell that is only at one tap. The branch pipe may hold stagnant water.
Safety
A smell may signal poison, and a tank that smells is a confined space
Do not drink water that smells of fuel, solvents or chemicals, or that carries an oily film, and do not boil or chlorinate it in the hope of fixing it: neither removes petroleum or most chemicals. Do not enter a tank, well or pit that smells of rotten eggs, because hydrogen sulfide can kill, and because it numbs the sense of smell. Enter only with 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: Simple Chemical Tests — measuring what the senses can only suggest
- Combine with: Source Investigation — tracing a smell to its origin