Just a note about rainwater as a non-potable irrigation source.

Read the following articles and do your own research before using rainwater as a non-potable irrigation source.  Generally, using rainwater as an irrigation source for vegetable gardens through drip irrigation or sub-surface irrigation techniques is considered safe.  Spraying non-potable water on leafy harvestable vegetables such as lettuce, broccoli, or cauliflower has risks, so read the following articles.  If you do spray leafy harvestable vegetables with non-potable water they must be washed thoroughly with potable water prior to eating them.  Non-potable water poses some hazards as spelled out in the articles below and care should be taken to insure your food is safe!  Make sure you have done your homework so you know how to use non-potable water in a safe and healthy manner!  If you are planning to use non-potable rainwater to water non edible flowers, shrubs, trees, and grass then it is perfectly safe for that purpose.

Is Rainwater Really Safe??  Click on the following link to find out more!
http://www.harvesth2o.com/rainwater_safe.shtml

Rainwater Harvesting- Water Quality and Health Risk
http://www.who.int/water_sanitation_health/gdwqrevision/rainwater.pdf

A Comparison of Potable Water to Non-Potable Water (Wikipedia definition)

Drinking water or potable water is water of sufficiently high quality that it can be consumed or used without risk of immediate or long term harm. In most developed countries, the water supplied to households, commerce and industry is all of drinking water standard, even though only a very small proportion is actually consumed or used in food preparation.

Typically, water supply networks deliver potable water, whether it is to be used for drinking, washing or landscape irrigation. One counterexample is urban China, where drinking water can optionally be delivered by a separate tap.

Over large parts of the world, humans have inadequate access to potable water and use (non-potable) sources contaminated with disease vectors, pathogens or unacceptable levels of dissolved chemicals or suspended solids. Such water is not potable and drinking or using such water in food preparation leads to widespread acute and chronic illness and is a major cause of death in many countries.