How much water falls on your area
When it rains ...
For every inch of rain that falls on a 1,000 square foot roof, you can expect to collect just over 600 gallons of water. If the average annual rainfall in your area is 30 inches your 1,000 square foot roof will gather about 180,000 gallons of rainwater per year.
The easiest way is to look at rain charts with average rain fall estimates. http://www.betweenwaters.com/etc/usrain.html
More specific information can be found here - http://countrystudies.us/united-states/weather/
You can also contact your local news weather office or go to their website
If you want really know the amount of water that falls on your own property you can purchase an inexpensive rain gauge. Some gauges are more basic than others. The more complicated gauges include a small bucket - which gets left out in the rain - and a small display which sits in comparative comfort indoors. The bucket communicates with the indoor display (via a wireless connection), and tells you exactly how much rain has just fallen. It also tracks the rainfall over the previous month.
All you need to do is write down the mm/inches that it says.
