I usually carry my paint-soaked brushes to the quiet shores of the city reservoir near my house, and swish them around in the water until they're clean as new. It doesn't cost me a cent, and no one knows the difference! Just a little dark, tree-hugging humor there. I've actually got a method for cleaning and storing paint brushes that's so earth friendly you'll even be able to stop using those evil Ziplocs for overnight storage.
You're correct that the typical method of washing brushes and rollers is a mini ecological disaster. About five gallons of water flows from the typical faucet each minute, so you can do the math for how much is consumed during a 10-minute brush rinsing. But throwing out your painting tools at the end of each day or storing them in plastic bags aren't very appetizing alternatives.
These tips were given to me by Earthpaint (www.earthpaint.net), a company here in Asheville, NC that makes biodegradable, non-toxic paintfor interior and exteriorand generally sells it in recycled containers.
1. Always use biodegradable, non-toxic paints. The typical solvent-based paints you get at the local hardware store contain volatile organic compounds, or VOCs, which emit pollutants that contribute to smog (and aren't very good to breathe). Besides, VOCs are adding nasty toxins to the sewer system every time you wash them down the drain.
2. For cleaning, take some recycled paper and blot the brush, without pressing or squeezing tightly, to remove as much paint as possible.
3. Take three five-gallon paint buckets and pour about two gallons of clean water into each one. Rinse the brush in the first bucket, swishing it around until all of the paint is free. Then swish it in the second bucket for a couple of minutes, until the bristles appear clean. Finally dip it into the third bucket, letting it soak.
4. Tap the brushon the metal part of the handle just above the bristleson the toe of your boot to shake out excess water.
5. Save the water in the buckets for tomorrow. You should get several days' use out of just those six gallons.
6. Don't drink the city's tap water if you see me near the reservoir with paint brushes in-hand.