Idea was originally posted by (Eccles) at Fluwiki
Beware Water From Roof Runoff
* Link Unavailable. This site is no longer active and available to view on line. But the info was good and we wanted to keep sharing it!
Since people are asking how to collect rain water without using the roof, here's a little on how I anticipate doing it. One needs to buy some large plastic or plasticized tarps (they are very cheap) and some metal fence posts (the kind used for chicken wire; they are also very cheap).
In my case, the tarps have eyelets at the corners and in the middle of each edge. We will use these to simply hook the tarp to the fenceposts as follows:
Set 4 fence posts up in a square arrangement to support the corners of the opened tarp, with the 'rear' posts holding the tarp up about 3-4 feet off the ground and the 'front' posts holding it up about 2 feet off the ground. Then rig additional posts to support the left and right edges. Rig a post to support the middle of the rear edge, and tie a string or rope to the middle eye in the front edge.
This setup will give you a tarp which is angled toward the front, and which has a 'Vee' crease down the middle to channel water to the front middle eyelet and edge. You capture the water here with buckets, tubs or anything else you have that will hold water and let you drag it off.
If we use an 8'—10 foot tarp, and if we allow for the reduction in capture area caused by the tilting and creasing, we are left with about 70 square feet of capture area. Now, when it rains, we will be able to capture a maximum of 42 gallons per inch of rain.
In other words, multiply 42 by the number of inches and you get the approximate amount of water you could get. With even a tenth of an inch of rain, you could get about 4 gallons this way. You could easily set such an arrangement up in a front yard, back yard or on a driveway.
A smaller tarp will deliver less water, and a larger one more. With a back yard of any size at all, you should be able to run several of these setups (well under $10 each for the materials).
Once you have captured the water, then treat and filter it as has been described in other threads.
You can use this water for drinking and personal washing. Use the downspout water for flushing.