Ecovie Rainwater Collection Systems

Rainwater Capture Potential

How much water can you collect from your roof?

It depends on how much it rains and how big your roof is, of course. But what surprises most people is how much water can be collected from just an inch of rainfall: each inch of rain on a 1,000 square foot roof translates into approximately 600 gallons of captured rainwater. This is the equivalent to 10-12 rain barrels.

Larger roofs, and especially roofs on commercial and institutional buildings, have incredible potential for capturing rainwater. Rainwater collection from other hard surfaces like patios and sidewalks adds to your totals, as does collecting the condensation from HVAC systems, which for commercial applications can add up to tens of thousands of gallons per year.

Below, for example, are two tables that show rainfall and collectable rainwater amounts in the metro Atlanta area over the past four years (for a residence and larger businesses, respectively. In the Atlanta area, even during the 2007 drought, Atlanta received 32 inches of rain --- from which PLENTY of water could have been collected.The second table shows Atlanta average rainfall and drought rainfall as compared to other cities.

Please let us know if you’re interested in data for other areas in the country and we’ll be happy to provide it.

Consider this residential example:

 

4,000 Square-Foot Roof Footprint
	Rainfall	Collectable Gallons
2007 Rainfall	32 inches	71,000
2008 Rainfall	41 inches	92,000
2009 Rainfall	59 inches	132,000
2010 Rainfall	47 inches	102,000
30 Year Average Rainfall	50 inches	112,000

 

For larger building, the potential is obviously more:

 

Roof (Square Feet)	Atlanta Collection Potential (gallons)*
	Gallons per Inch	2007 Totals	2010 Totals	30 Year Average
10,000	5,300	169,000	249,000	265,000
20,000	10,600	339,000	498,000	530,000
50,000	26,500	847,000	1.2 Million	1.3 Million
100,000	53,000	1.7 Million	2.5 Million	2.6 Million

* assumes 15% loss due to evaporation and other factors

What About Summer Rainfall?

We hear many comments that collecting rainwater is all well on good here in Atlanta, but in the summer it never rains.  While it’s true that we can go many dry days without rain, Atlanta is blessed with heavy rainstorms that fill our tanks just when we need it.  In fact, during the 5 years 2004 through 2008, monthly summer rainfall in Atlanta has actually increased during summer months. And, if you are using rainwater indoors during the winter, there is plenty of water to meet all needs.

Furthermore, did you know that Atlanta receives on average more rain than Seattle or Portland? As a result, rainwater collection can provide most or all water needs for the typical family household. In the arid parts of the US, rainwater collection is starting to be REQUIRED for indoor non-drinkable water uses such as toilet flushing and laundering. Even with very low rainfall, these areas are successful at using rainwater for these purposes.

 

	Average Annual Rainfall 1970-2001 (inches)
New Orleans	64
Miami	59
Memphis	55
Atlanta (1970-2001)	50
Charlotte	44
New York	43
Boston	43
Atlanta 2008	41
Cleveland	39
Seattle	38
Pittsburgh	38
Portland, OR	37
Chicago	36
Milwaukee	35
Dallas	35
Detroit	33
Atlanta 2007 Drought	32
Minneapolis-St. Paul	29
San Francisco	20
Denver	16
Los Angeles	13
Phoenix	8
Las Vegas	3

 

The upshot is that Atlanta has plenty of rain for rainwater harvesting even when it does not rain as much as we are used to!  Other areas likewise have a lot of rainwater harvesting potential.