The main water tank outside is 1500 gallons, the reserve tank is 400 gallons. We get about 600 gallons to 1 inch of rain from our roof space. The main roof is 20' x 48', the second story roof is an additional 16' x 20'. We have water flow restricters and a low water flush toilet in use in the house. It's just like the city, but the water comes from the rain, not a pipe via the water treatment plant. Our area receives enough rain to get us through the year. The reserve tank is usually pumped into the main tank in late august to tide us over the end of the dry summer in Oklahoma. I don't have a washer or dryer at the house, i go to the laundromat in town. If we put in a larger tank, we could support a washer, we get enough rain, it's just something we've never bothered doing as laundry isn't my favorite thing. I can get a week of laundry for 4 people done in 2 hours at the laundromat, i find that easier.
The water goes through a whole house filter before it goes into the main line to the rest of the house, we also add some regular bleach to the outside tank occasionally. The water is so soft, that soap and shampoo wash away quicker than with water from the city. The sinks and bathtub are on separate drain lines that go out to the front brushy area to reuse the gray water. The toilet goes to a modified septic leach pond area.
I think I labeled everything so it is easy to understand, I had to ask my husband to help me label all the parts as I'm not the plumber.
I hope this will help other people who live in areas without a water line to hook into, or those who can't have a well due to polluted water tables.
Post any questions, i'll try to answer them. Thanks for checking out my instructable!