Depending on where you live and what type of system you wish to utilize, there may be resources available to you to help offset your costs.  For example, the Marin Municipal Water District has a rebate program:

Replacing older toilets and clothes washers with new high-efficiency models is an easy way to trim your water bill and help conserve our precious water resources. The MMWD even pay you to make the switch!

Get up to $150 each for EPA WaterSense labeled toilets (Limit: two per household)
Get up to $150 for an Energy Star Most Efficient clothes washer

 

Other MMWD rebates also exist:  check out https://marinwater.org/rebates

 

The Sonoma County Water Agency also provides links to additional resources: http://www.scwa.ca.gov/residential/

For farm or landscape level resources, please check the information on our Rain Catchers in the Watershed page.