In determining your tank size, first check the history of average annual rainfall in the area for the last 100 years or the longest period available. This information is usually available from the Bureau Of Meterology. It is important to also determine on average, the longest periods without rainfall. Some areas get a great deal of their yearly rainfall at a particular time of year. To satisfy such a situation, a larger storage capacity would be required.
When it becomes clear that you're facing a prolonged dry period, it is important to moderate water usage giving consideration to the water you have on hand.
