Most rainwater currently drains to the street and enters Zimpher Creek (undergrounded) via storm sewer, and then on to the Laguna de Santa Rosa. Less runoff is currently retained than when we purchased the house due to our attempt to reduce the amount of water flowing under the house, particularly during major storm events. The house was built on fill over a shallow swale that still carries water underground down the old watercourse. We now have a crawlspace seal and sump pump from Clean Crawlspace, Inc., which has made a huge difference in the amount of moisture under (and inside) the house. We created a passive drain to prevent flooding at times the power is also out for an extended time during those major storm events (once or twice a year).

The lawn area below the house was installed over the former driveway, which created a fairly impermeable layer below the turf. As a result, water pools during storms, but tends to run off.

Rainwater collection calculations indicate that we could harvest over 20,000 gallons annually for our 1050 sq. ft. roof! That amount is well above what we use for gardening, toilet flushing, bathing and laundry. With filtration, it could provide drinking water as well.

Steps to take for rainwater infiltration

  • Remove turf and underlying rock
  • Create an infiltration swale bounded by existing fruit trees and other plantings
  • Steps to take for rainwater harvesting for domestic/landscaping use
  • Metal roof appropriate for water collection
  • Current roof is composition and asphalt shingle. It will need to be replaced within two years. I would like to do some remodeling at the time to allow better insulation for two small flat-roofed additions built in 1938 or earlier.
  • Water storage tank and collection system
  • Area adjacent to house could be utilized. Since the lot slopes only slightly and the available space is on the downhill side, a pump would be required (could be solar-powered)

Greywater use

Shower/bath water run during warm-up and sink water could used for landscape and fruit tree irrigation. Laundry water could be used also, though water needs more treatment. Soaps, debris buildup, man-made fibers and possible pathogens would be issues. We could easily overwhelm our current plants with greywater from laundry alone and we would not typically need the extra water from November-May.

Steps to greywater use

  • Install tank for gravity feed
  • Modify plumbing to include valves and bypass pipes from the various water sources
  • Install filter system, particularly if using laundry water
  • Modify irrigation system for deep irrigation (drip system is currently surface only)
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