What does foam and color say about water quality?

Bjorn,

Looks can be deceiving. For example, in Death Valley, USA, there are some crystal clear springs. They are clear because they're contaminated with heavy metals.

I don't know of anyone who ever got sick from filtering, or otherwise properly treating their water. I do know people who got sick from drinking water they thought was safe.

Most foam is caused from breakdown of organic matter and swirling of water which mixes it with air. A lot of those oily sheens you see in bogs and marshes are also caused by organic matter. I'm sure some more knowledgeable biologists will have more to add, although I once was on a hike with a person that was supposed to be knowledgeable about such matters and they thought it was pollution.

Your foam picture does seem a little unnatural looking, but I see a lot of organic matter and the stream appears to be splashy.

A yellow or brown color can be from leaves or other organic material or from harmful pollutants. The only ways I can think of to know if chemical pollution is present is to send the water to a laboratory or to know what sources of pollution are present in the area now or in the past.

Neither chemical treatment (aqua mira) nor filtering with backpacking filters will remove much chemical pollution.

We paddle a fair bit and therefore see all sorts of water conditions. Tom is right about the organic matter that causes the foam. I have some information on it kicking around here somewhere so I'll dig it up – I can't remember exactly what type of algae or organic substance it was off the top of my head.

Some of the water we encounter is the color of tea. Other water has a greenish hue. Some lakes, like the acid lakes in some parts of Killarney Provincial Park and the Chiniguchi region, are crytal clear and pretty blue because they won't support any life at all.

Because you can't tell how safe water is by the look of it – just be careful and treat/filter your water.

Chemical pollution, as others have said, can't be removed. That isn't generally an issue where we hike or paddle though.

Yellowy brown with foam is often a sign the water has come of peaty moorland. Not too harmful, but I filter it because of the risk of sheep and badger diseases. If it looks super clear, I just run it through my 2oz premac military water filter anyway. Can't have a bad stomach ruining a trip.

Just to clarify, I always threat the water with micropur + aquamira frontier pro (just because you never know if an animal has pooped in upstream), but despite of that I still chose my water sources. When reading the comments I find that color and foam will not disqualify the water from threating and drinking in advance.

If I was up the hill I would treat and drink peaty coloured water. Down in the valley, I would seek local knowledge, and probably some clean water supply.

Some plants actually contain a surfactant which can cause foam under a small cascade. Clean white foam in flowing water in a wilderness environment is probably just that.
Dirty foam … Hum.

Brown/yellow colour in a wilderness environment is very often tannin from decomposing vegetable matter. In some places (eg SW Tasmania) the colour is very dark. Quite harmless.

Greenish colours near farms or housing … treat as toxic!

Clear water without any little animals or bugs – may have high levels of metals. Downstream of mining this is common. You can even get Arsenic downstream of old silver mines.

Cheers