Photo Clive Nicholson, CC BY-SA 2.0
Water not to drink
Salt water, scummy ponds, runoff below mines and roads, and the other water that boiling and filters will not fix.
What to leave alone
- Salt water from the sea or a salt marsh
- A pond or lake with a green, blue or brown scum on it, or water that looks like pea soup or spilled paint
- Water below a mine, a quarry, a dump or old tailings
- Ditches and runoff beside a road, a railway or a parking lot
- Water below farms, pastures or a cabin outhouse
- Water with a dead animal in it or just above it
- Water with an oily sheen, a chemical smell or foam that does not break up
- Urine, and alcohol of any kind
How
- Before you fill up, look upstream. Ask what is above you.
- Go above the road, the camp or the trail crossing and fill there.
- Pick moving water over still water, and clear over cloudy.
- Look at a pond before you drink from it. If it has scum, a strange colour or a bad smell, walk on.
- Then treat what you take, every time. See Making water safe.
Do and don't
Do
- Carry enough from a good source to get you to the next one.
- Watch for posted notices at a pond or lake about an algae bloom.
- In doubt, go without a little longer and find better water.
Don't
- Do not drink sea water, not even a little mixed in. It takes more water out of you than it puts in.
- Do not count on boiling or a filter to fix a bloom, a chemical or salt. Boiling kills germs. It does not take out poisons, and it can make them stronger as the water boils away.
- Do not let dogs drink or swim in a pond with a bloom on it.
Watch for
Danger
- Some algae blooms make poisons that can hurt the liver and the nerves. Sickness, cramps, diarrhea, tingling or weakness after drinking pond water is serious. Call 811, or 911 if it is bad.
- Thirst makes bad water look good. Decide what you will not drink before you are thirsty.
Notes
Most bad water in the country is bad because of germs, and boiling or a good filter handles that. This page is about the rest, the water no pot and no filter will make right.
If the only water you can find is on this list, the answer is to keep moving to the next brook, not to drink it.
Updated 2026-09-27
Related
Making water safe
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Boiling, filtering and treating water so it does not put you down.
Carrying and storing water
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How much to carry, what to carry it in, and how to keep a supply at camp or the cabin clean.
Catching rainwater
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Turning a tarp, a roof or a tree into a water source when it rains, and keeping what you catch clean.
Finding water
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Where the water is when there is none in front of you.