You may want to harvest rain to drink because you don't want to pay utility bills, or maybe you don't like the taste of your municipality's water. Whatever the case, drinking rainwater can wash down quite smoothly if done right. Collecting rainwater is required in areas throughout Australia. Beware that rainwater can contain insect parts, pollution and radioactivity, so you will need to treat it before consumption.
Put a barrel or other catch basin at an area under your roof where water falls. Alternatively, you could leave the basin in an open area outside, but you will catch less water.
Position a "first flush diverter" at the location where the rainwater enters your catch basin. The devise is a filter that will stop roof debris such as leafs and insects from entering the basin. Store the water in a tank until you need it.
Pour the water into a portable container and boil it. Run it through a refrigerator water filter, such as a Brita, before consuming. Alternatively, you can place a pump in the tank, and run the line to your house's plumbing. You will need to hire a plumber to do this.
Install roofing without lead, chromium, cadmium, soldering, flashing and paint. Coated metal roofs can also make rainwater toxic.
Add water purifying chlorine if you want to be extra cautious about the quality of your water.
You may want to have your rainwater tested by a laboratory.