Do you have a lawn that you water? How about a garden.  
Do you wash your vehicle at home?  
Do you shoot down your driveway, or lanai, sidewalk when it's muddy or dirty?
If you do any of these, your home adds to the water burden.  Don't agree? Here's a crude example.
Condo may have a grassy area in the complex for 100 families, 100 homes with lawns will use more water then the grassy area the condo has daily.