Rain Water Collection Converting inches of rainfall into gallons of potential irrigation water

Rain Water Collection In most landscapes rainfall is diverted into drain lines and directed through a hole in the curb then flushed to the sea as quickly as possible

Rain Water Collection Most any flat, impermeable surface within a landscape can be a source of potential, future, irrigation water Definition: impermeable—not allowing fluid to pass through

Rain Water Collection This includes: Rooftops using rain gutters and downspouts Patios & patio covers Driveways & sidewalks

Rain Water Collection Water from these flat surfaces can be channeled and captured in large, closed collection tanks for future use

Rain Water Collection The most typical flat surfaces include: Roofs Patio covers Patios And walkways

Rain Water Collection First – determine the potential for water savings per year Ex. water costs in Westminster are $2.29/unit (as of summer 2012) 1 unit = 100 cu.ft. of water or 748 gallons of water

Rain Water Collection My bill for 3 residences averages about 18 units/month or about 13,464 gallons per month For 6+ people 3 toilets 3 kitchen sinks 3 tub-showers And whatever yard watering

Rain Water Collection We average about 14 inches per year of rainfall in the Orange/LA County areas (more or less) How much usable, potential irrigation water does that amount to?

Rain Water Collection Let’s say we have a storm that deposits 1” of rainfall on your roof and your roof covers 1,000 square feet of area How many gallons of water does that amount to?

Rain Water Collection The first thing we need to do is to convert the amount of rainfall into a comparable measurement—to something we get billed for

Rain Water Collection We start by asking ourselves: “How many gallons of water are there in 1” of rainfall over an area of 1,000 sq.ft.?”

Rain Water Collection Since we are ultimately dealing with cubic “FEET” of water – we should probably begin by turning inches of rainfall into “FEET” of rainfall

Rain Water Collection So 1” of rainfall equals how many “FEET” of rainfall? 1 foot = 12 inches so we could divide: 1” rainfall = ft. 12”/foot (don’t forget the inches cross-cancel and feet come to the top) So 1” of rainfall = ft. of rainfall

Rain Water Collection Next figure out just how many cubic feet of rainfall in our 1000 sq.ft. area that amounts to: Remember that cubic feet represents a volume Volume = Area x Depth or V = L x W x D provides an answer in “cubic ‘something’” Remember: Area = L x W

Rain Water Collection So if we take the area (in sq.ft.) covered by rainfall and multiply it by the depth of rainfall (in ft.) that will give us the amount of cubic feet of rainfall Volume = area x depth (V = A x D)

Rain Water Collection We started with an area of 1,000 sq.ft. covered by rainfall and ft. of rainfall 1,000 sq.ft. X ft. = 83.3 cu.ft. of rainfall

Rain Water Collection How many gallons does that convert to? Since there are 7.48 gallons per cubic foot of water We could divide: 7.48 gallons/cu.ft. X 83.3 cu.ft.= gal. 1 cu.ft. (don’t forget the cu.ft. cross-cancel)

Rain Water Collection So... For every 1” of rainfall on an impermeable area of 1,000 sq.ft. we could conceivably collect 623 gallons of possible

Rain Water Collection And in an average year, with an average of 14” of rainfall, that means about 8,727 gallons per year of potential irrigation water! Almost 12 units per year Or about $28 year Is it worth it?

Rain Water Collection Now how much water does that lawn need to stay green? On average of about 1” of irrigation per week Or 624 gallons per 1,000 sq.ft. per week At 38 weeks per year (arbitrary number assuming 14” of rainfall over 14 weeks)

Rain Water Collection That’s about 25,000 gallons of irrigation water per 1,000 sq.ft. of lawn per year About 33 units per year About $75 per year

Rain Water Collection It probably wouldn’t be practical to irrigate lawns using captured rainfall It might make sense to use that captured rainfall in a “gravity fed” drip system in the planters Wouldn’t that offset water costs for residential landscape irrigation uses?

Rain Water Collection The costs may not sound like much now, but water rates continue to rise! The future price of tap water: Tap water = bottled water That might make it worth it.

Rain Water Collection