Water Footprint is a Dutch site that allows consumers to estimate the water consumption that is embedded in other kinds of consumption. As a student of coffee, I was particularly interested in the 1100:1 ratio between coffee and the water needed to prepare it. Although coffee requires almost 1.3 meter of rainfall per year, this accounts for only about 1/7 of the total, as water is needed at many stages.
The water used in the coffee is renewable -- it does not disappear or anything. But a lot of it is used in locations thousands of miles from the consumer and with minimal environmental regulations. Because the water used for growing will return to local streams and water supplies, organic coffee can help to keep those resources free of pesticides and fertilizers.
Similarly, the water used for depulping is usually returned to local streams, full of nutrients that can lead to algae blooms and diminished available oxygen for fish. For this reason, it is important to support integrated production systems that harvest biogas or otherwise capture the nutrients before returning water to the local environment.
This page is an overview of the group's findings regarding coffee and tea. It includes links to more detailed studies (in Dutch and English) of each.