Unlike most folks we have no well or city water.Our shack water is collected from the gutters and goes into a 1700 gallon cinder block cistern. This water serves for our household and critters however we do not drink it. For our drinking supply of water we use our spring here on the property.
Our cistern here on the homestead is made of cinder block and then coated to be water proof. Part of the shack has a gutter system to collect the water from a rain and then run it through pipe into a set of screens and then down in to the cistern. We have a small pump that then pumps the water into the shack. However if needed we could hook a pulley system over the cistern and pull the water out by the bucket or use a small gas powered pump that we have. To most this would be a daunting task, to us it would be next no extra hassle as we dont use much water.
The cistern holds about 1700 gallons so it is not a huge cistern as compared to some. It does however, do a pretty good job of fulfilling our needs. I am sure our 70-80 inches of rain a year is much of the reason we are able to get by on such a small cistern, as it is always or nearly always getting replenished. We are also very conservative of our water usage and only use about a 100 gallons a week for all our needs. I have been slacking and taking laundry to town when we go but if I do wash here it is about another 20 gallons a week of water that we would use. All the animals water comes from separate rain barrels. Even in the summer, on the rare occasion that we need to water the garden, our cistern is able to keep us with plenty of water. The only times it wasn't able too was because of human screw up or when we had(too) many people here during drought. We do haul water from the pond when it becomes necessary.
so how much rainwater can you collect
To figure out how much rainwater you can harvest just multiple the square footage of roof space you have available X 0.6 gallons per square foot per inch of rain, and you can see how much water you can collect from each inch of rain that falls.
For a more in depth article on rain water calculation http://www.docstoc.com/docs/17688019/How-Much-Water-Can-You-Collect-in-Rain-Barrels-During-a-Rainfall.
for ideas on rain water harvesting