One of the great accidental discoveries I have made in the last few years is how to get free distilled water. My forced air furnace (any forced air furnace) has a drain that goes throuh the wall and outside. Has an elec. heater inside of it so it won't freeze during the winter. Only time water comes out this drain is in winter anyways, your central A/C has a seperate drain line. My heater died, water started showing up in the hall carpet. Now, I have that drain line rerouted. I even used the existing drain pipe, just redirected it. You can have your furnace repair guy do this on a simple service call if you don't want to do it yourself. Plugged up the hole going outside, of course. Now my drain line comes out of the furnace about 3' off the floor. There's a 5 gal bucket under it. Free distilled water. Not sure I'd use it for drinking but it is ideal for watering plants (if you live in the city or just don't trust what comes out of the faucet.) I live in the country so I do not use my free water for that. Instead, I use it in my humidifiers. Have been through many different types of humidifiers in the last few years and the secret is to use distilled water in them. I'm too lazy and cheap to go buy water. Works great. What the humidifiers use and what I get out of my bucket comes out about even. I do keep the indoor humidity between 45-50% in the winter. Nice for me and my plants. In the fall, watching the water level in that bucket gives me a good idea of when I need to start running my humidifiers. In the fall before I run my humidifiers, I save the water in gal. jars, just in case I need extra later. I always have about 15 gallons of water sitting around just for emergencies: power out, water plants, fill fish tank, flush toilets, etc.
gasrocks, fortunately I have a well for my water supply home and garden. I understand the need for quality water for watering your plants, but I would not trust the purity of this water for anything else other than your car battery. I have modified my roof drains to collect rain water much like they do in Mexico City. I am an environmental chemist and some years back I worked with a hydrologist who spent a month each year in Mexico teaching about water supplies. Their flat roof homes were a great source of collecting rain water when it did rain, so they built underground cisterns to collect and store this water. But the same rule applies to all water supplies if you happen to be traveling in that direction...DON'T DRINK THE WATER!