If you live in a community with alluvial sandy soils and depend on imported water from the Delta or the Colorado River, then it is critical that you water your lawn to recapture some of that imported water for reuse rather than let it evaporate or run to the ocean. The only way to recharge local groundwater basins is by watering vegetation. Sewer water runs to huge treatment plants and can be reused. The recharge rate used by hydrologists is 15% per year from watering residential vegetation.

During droughts watering must be curtailed but in wet years it is very critical to water lawns to recharge basins so that there is water storage for dry years.

However, if you live in an area with clay or sandstone soils, there is no percolation of water possible and watering lawns would be of no help.

No help either to water lawns in communities that are self-sufficient on their own groundwater such as Downey in Southern California that doesn’t depend on imported water.

Instead of building expensive water recycling plants it is better to just water your lawn if you live on sandy soil and get water from the Delta or the River.