There are ways of capuring rainwater or waste greywater. Some of these can be expensive but often the best options are simple and low cost.
Reusing Rainwater and Greywater - Centre for Alternative Technology
Reusing Rainwater and Greywater - Centre for Alternative Technology
How to save water - CAfS
Reusing Rainwater and Greywater - Centre for Alternative Technology
How to save water - CAfS
Reusing Rainwater and Greywater - Centre for Alternative Technology