Can You Drink Rainwater?

Of course. People have been collecting and drinking rainwater for centuries.

Is it legal to collect rainwater at your home and drink it? Yes, but if you want to keep yourself and your guests healthy, some level of treatment is necessary. Here are the steps in a modern rainwater collection and treatment system:

1. Prefilter. Keeping the leaves and sticks out of the cistern is the most important step to keeping water safe. Any significant amount of organic material will eventually go septic and make the water stinky.

2. Cistern (tank). Keep the water cool and dark, so that algae and mosquitoes don't grow.

3. Cistern Piping. Prevent mosquitoes from leaving, and critters from entering. Bring new, freshly aerated, water in at the bottom of the tank, without stirring up any debris at the bottom.  Pump outlet piping should be a few inches off the bottom.

4. Final Treatment. We recommend a combination of carbon filtration and UV sterilization. Chlorine isn't necessary with this pair, but it can work instead of them. There are some problems with chlorine in general, and getting the right level is tricky. So we recommend carbon and UV.  A sediment filter upstream of the carbon and UV helps the carbon last longer.

Drawings and other resources are here:
http://www.georgiawatertanks.com/rainwater-harvesting-detail-drawings-cad.html

Is It Illegal to Collect Rainwater?

Short answer, NO. For any state other than Colorado, rainwater harvesting is LEGAL.

Even Colorado allows 2 - 50 gallon rain barrels.

Another example often giving is a person in Oregon who built 3 PONDS on his property without getting permits. Dam permits are required in most states, so that's not unusual.

Other than that, rainwater harvesting is permitted, even encouraged. Providing that you get the required building permits and follow building codes.

For our usual recommendations for rainwater harvesting at your home, see
http://www.georgiawatertanks.com/residential.html