Tag Archives: raingarden

Residential Rainwater Collection

Cement Cisterns Collect Urban Rainwater

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With limitedspace in urban areas, cement cisterns are being built beneath homesas a rainwater harvesting solution.

A narrow, covered passage with a person lying inside.With the new “Green Storm Water Infrastructure” or GSI mandate, Seattle based RainBank Rainwater Systems is seeing increased interest in rainwater collection. But, with limited space on an urban building lot, the storage of rainwater in above ground tanks is not an option when required to mitigate thousands of gallons of roof runoff.

With many new residential construction projects building on small city lots, there is just not enough room for a rain garden. One way to solvethis issue is with a cement vault, constructed beneaththe house, which stores the captured rain water for potable use.

The average 2,000 square foot roof area will yield over 44,000 gallons of water. However, a cement vault cistern needs special engineering and considerations. Water weighs approximately 8 lbs per gallon and 1 cubic foot equals approximately 8 gallons. Calculations of weight and sheer need to be engineered for Seattle’s seismic zone. Additional ventilation should be considered along with aeration.

Person spraying concrete or plaster on a wall in a construction setting.Cement water tanks are not naturally waterproof; cracks in concrete can resultyears after construction. The use of a liner, whether spray on epoxy, or a poly bag will prevent groundwater from entering the water tank as well as improve water quality.

Commercial Rainwater Harvesting, Rainwater Catchment, Residential Rainwater Collection

How to Offset Costs of Stormwater Regulations for New Construction


Workers installing large septic tanks at an excavation site.New stormwater regulations forrunoff and green storm water infrastructure are adding to the costs of new residential and commercial construction in Seattle and elsewhere. Infiltration of runoff from roofs, driveways, and all impervious surfaces are mandated by local and Federal agencies. While infiltration does help reduce storm water runoff, the added costs of implementing infiltration or a rain garden can be considerable, with no return on investment for the home owner or building’s owner.

By directing costs of designing and implementing an infiltration system or rain garden to a rainwater collection system, the builder can mitigate stormwater runoff to a useful purpose. Irrigation, toilet, laundry facility, and whole house (potable) usage can be supplied by rainwater collection, storage, and use, lowering monthly water and sewer bills.

The Seattle times recently reported on rate increases over the next 5 years for water and sewer, to meet the challenges of expansion and repairs to an aging infrastructure. Approximately 6.2 billion dollars are expected to be needed over the next 20 years for expansion and repairs to the existing infrastructure in the Puget Sound region as a whole.

Row of rain barrels connected to a gutter system for water collection.While the average monthly billing increases are not enough to pay for a rainwater catchment system, the costs of designing and implementing an infiltration system or a rain garden are significant enough that if redirected to designing and building a rainwater collection system along with lower water and sewer bills, a homeowner or building owner will recognize a return on investment.

A well designed and implemented rainwater harvestingsystem for toilet and laundry facility for a single family residence can save 49% of their city water usage with a small amount of storage. Using the available water from roof runoff rather than just infiltrating it into the ground makes a lot more sense and has a return on investment.