This method to filter rainwater has been around for more than 100 years. It is tried and true. Once you collect rain water in a barrel you will want to filter it.
If you have a rain-collecting system in place then use this old method to safely and easily filter the water you collect.
Believe it or not it may not be legal to collect and use the rainwater on your property. Check with your officials. But if you do collect rainwater in a barrel, this filtering method has been around a long time and still works.
I found this article from our friends at ThePrepperJournal where you can read more in detail.
For gardening, rainwater is, naturally, best unfiltered. But, for household use, the vintage book says the following instructions yield a cheap and easy way to make a filter just as good as a patent filter costing 10 times as much:
Take a new vinegar barrel or an oak tub that has never been used, either a full cask or half size. Stand it on end raised on brick or stone from the ground. Insert a faucet near the bottom. Make a tight false bottom 3 or 4 inches from the bottom of the cask. Perforate this with small gimlet holes, and cover it with a piece of clean white canvas.
Place on this false bottom a layer of clean pebbles 3 or 4 inches in thickness; next, a layer of clean washed sand and gravel; then coarsely granulated charcoal about the size of small peas. Charcoal made from hard maple is the best.
After putting in a half bushel or so, pound it down firmly. Then put in more until the tub is filled within 1 foot of the top. Add a 3-inch layer of pebbles; and throw over the top a piece of canvas as a strainer. This canvas strainer can be removed and washed occasionally and the cask can be dumped out, pebbles cleansed and charcoal renewed every spring and fall, or once a year may be sufficient.
This filter may be set in the cellar and used only for drinking water. Or it may be used in time of drought for filtering stagnant water, which would otherwise be unpalatable, for the use of stock. This also makes a good cider filter for the purpose of making vinegar. The cider should first be passed through cheese cloth to remove all coarser particles.
Or a small cheap filter may be made from a flower pot. A fine sponge may be inserted in the hole and the pot filled about as directed for the above filter. It may be placed in the top of a jar, which will receive the filtered water."