Hi, Sorry that I'm new at this so I don't have the practical experience.

But I think this is a more general question about water quality of a stream and what you might find in it that might be bad:

It really depends. If the stream is a rare underground aquafer (naturally filtered) source you could be feeding your plants Perrier which could be great. But otherwise, surely you have microorganisms under control. The problem is going to be what potentially toxic runoff is going into there.

You need to know the source of the waters and what lands they travel through to get to you, otherwise who knows. Rivers have been used for irrigation since the beginning of agriculture, but if it runs by the landfill that could be a problem.

Why not just buy a 55 gallon plastic PE drum and make a rainwater catcher, then just worry about what's in your roof or make an appropriate collector to catch it.

I'm assuming that you want to recycle the nutrients and this is hobby sized (even big hobby sized), so it sounds like a lot of work to go through and to be worried about PCBs or heavy metals. Of course if you live in the high Colorado Mountains and not Hudson Falls, NY, you can probably drink from most of those rivers without any worries!

One thing to do that's free- call your local cooperative extension office and maybe water management district and ask them about the water quality.

Good luck! You can never know and the only sure way especially if you live in a highly industrialized area is to have the site tested by an environmental lab. The low ppms probably mean a lot of rainwater, but remember the toxics are in the ppb's. Ask any local farmers, if there are any, they may already know the answer.
-Pupilla

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I use rain water.

I first used a 55 gallon drum and it over flowed with the first storm of Rainy Season. Now I use a 275 gal IBC container that is off the ground far enough to gravity feed a Reservoir change. I keep redesigning my set up make it easier to clean and change water.

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