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How A lot Rainwater Can I Gather?

The need to gather rainwater can shortly flip into an obsession for many individuals on the market. Nonetheless, it could look like a problem to others, particularly these not sure about its price.

Regardless of the case could also be, you’d be stunned by how a lot rainwater you possibly can accumulate!

So, how do you calculate rainwater assortment?

The quantity of water you possibly can catch relies on how giant your catchment space is. For instance, most rainwater techniques accumulate rain from your private home’s roof. Nonetheless, you may also accumulate rainwater off impermeability surfaces, like your driveway or pavement.

By now, you’ll discover that some calculations are so as. However don’t fear, it’s not rocket science!

This text will have a look at the mathematics you’ll must calculate how a lot rainwater you possibly can accumulate. We may also information you thru the method with easy-to-follow examples.

Get a pen and paper out — let’s get began!


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How Do You Calculate Rainwater Assortment?

The common American residence can accumulate round 40,140 gallons of water a 12 months – that’s nearly an Olympic swimming pool! For you, this quantity will depend upon the typical rainfall in your space and the scale of your private home.

Earlier than we have a look at these various factors, let’s have a look at the equation we’ll use for the calculations.

Roof space (sq.ft) x inches of rainfall x 0.623 = collected water

Chances are you’ll be questioning why we’ve included an element of 0.623. Because the roof space is sq. ft and also you measure rainfall in inches, you’ll must multiply it by 0.623.

Moreover, we’ll assume that the system has an 0.8 yield — which means that you simply’d solely catch 80% of precise rainwater.

(rainwater collected) x (yield) = precise assortment

As you possibly can see from the above equation, some components are particular to your private home and placement. These are the realm of your roof and the inches of rainfall in your local weather.

Within the USA, the typical home dimension is 2,598 sq. ft, and the typical rainfall is 31″ yearly.

How To Discover The Common Rainfall In Your State

The different rainfall regions in the United States of America.
The completely different rainfall areas in the US of America.

These days, you not want a rain gauge to measure the quantity of rainfall in your space. Whereas a rain gauge is likely to be extra correct, a fast google search can provide the data you want.

In response to the Nationwide Facilities for Environmental Info, the typical rainfall in 2010 was 31 inches yearly.

For those who’re in search of a extra particular information set, you possibly can consult with this desk:

State Common Rainfall (in inches)
Alabama 56″
Alaska 31″
Arizona 22″
Arkansas 50″
California 22″
Colorado 17″
Connecticut 50″
Delaware 45″
Florida 50″
Georgia 48″
Hawaii 49″
Idaho 18″
Illinois 41″
Indiana 42″
Iowa 32″
Kansas 33″
Kentucky 47″
Louisiana 60″
Maine 40″
Maryland 44″
Massachusetts 43″
Michigan 34″
Minnesota 32″
Mississippi 57″
Missouri 41″
Montana 15″
Nebraska 27″
Nevada 10″
New Hampshire 46″
New Jersey 45″
New Mexico 13″
New York 37″
North Carolina 48″
North Dakota 17″
Ohio 40″
Oklahoma 36″
Oregon 75″
Pennsylvania 43″
Rhode Island 44″
South Carolina 48″
South Dakota 23″
Tennessee 52″
Texas 27″
Utah 17″
Vermont 43″
Virginia 44″
Washington 73″
West Virginia 45″
Wisconsin 34″
Wyoming 11″
These findings are common, in keeping with our analysis. Varied outcomes rely in your supply.

The desk exhibits the annual averages for rainfall within the state. Nonetheless, some components of the state will obtain extra rain than others. Subsequently, you need to use this web site to seek out out the typical rainfall in your metropolis.

It’s additionally essential to notice that these are annual averages. Each local weather has wet and dry months; you’ll accumulate extra rain in moist seasons.

How To Calculate The Space Of Your Roof

In response to CNN, the typical dimension of an American residence has grown by 150% since 1980. At this time, the typical space of a house is 2,598 sq. ft.

You need to use this common to calculate how a lot rainwater you possibly can accumulate. Nonetheless, for correct estimation, you need to calculate the realm of your private home.

This equation is straightforward – all it’s a must to do is multiply the size of your private home by its width.

Size x width = sq. footage

The difficult half is when your private home is irregular. That will help you out, we’ve created an instance of the calculation under:

An example of roughly measuring your roof's area.
An instance of roughly measuring your roof’s space.

L x W = Sq

You’ll must measure all of your partitions on the outside facet. Then, add all of the ‘widths’ up and the ‘lengths’ up. Ensure to not add any doubles and take away destructive areas like gullies or service shafts.

Professional Tip: Whereas it is a good begin, your roof additionally has overhangs. This implies the roof space is barely bigger than the footprint of your private home.

How A lot Rainwater Can I Gather From My Roof?

Subsequent, we’ll stroll you thru calculating how a lot rainwater you possibly can accumulate. One of the best ways to do that is by exhibiting you some examples which you need to use as base calculations.

We’ve three examples, a median residence from Carson Metropolis, Sacramento, and Salem.

Carson Metropolis

In Carson Metropolis, the wettest month tends to be February, with a median rainfall of 1.57 inches. Moreover, the annual common is 11.8 inches. So we’ll use these two valves in our calculations. 

First, let’s calculate how a lot rain a 2,598 sq. ft. residence can catch yearly. 

2,598 x 11.8 x 0.623 = 19,099 gallons

Moreover, we are able to calculate a yield of 0.8:

0.8 x 19,099 = 15,279 gallons

Subsequently, you possibly can count on to gather 15,279 gallons of water per 12 months. 

Subsequent, let’s see how a lot water you possibly can accumulate in February alone, excluding snow. 

2,598 x 1.57 x 0.623 = 2,541 gallons

With a 0.8 yield:

0.8 x 19,099 = 2,033 gallons 

Subsequently, you possibly can count on to gather 2,033 gallons in February. That’s sufficient water to flush a dual-flush rest room 635 instances or water a 32 sq. ft. backyard 100 instances. 


Sacramento tends to have a median annual rainfall of 16 inches. Its wettest month is January, with 3.64 inches of rain.

Yearly, a 2,598 sq. ft. residence can catch 20,718 gallons of rainwater. 

2,598 x 16 x 0.623 = 25,898 gallons

With an 80% yield:

0.8 x 25,898 = 20,718 gallons

As well as, a median residence in Sacramento will accumulate 4,713 gallons of rainwater in January. 

(2,598 x 3.64 x 0.623) x 0.8 = 4,713 gallons

In response to Harvard, that’s sufficient water to bathe for 31 hours.


Oregon is without doubt one of the wettest states in America, with Salem having a median of 44.9 inches of rain per 12 months. As well as, there may be a median of round 6.86 inches of rain over December.

Yearly, a 2,598 sq. ft. residence can catch 20,718 gallons of rainwater. 

2,598 x 44.9 x 0.623 = 72,673 gallons

With a 0.8 yield:

0.8 x 72,673 = 58,138 gallons

As well as, a median residence in Salem will accumulate 4,713 gallons of rainwater in December. 

(2,598 x 6.86 x 0.623) x 0.8 = 8,883 gallons

With 8,883 gallons of water, you would run your dishwasher 95 instances. Moreover, in keeping with the EPA, you would backyard with 8,883 gallons of rainwater for 3 months. 

Remaining Ideas

How a lot rainwater you possibly can accumulate relies on the scale of your private home. Moreover, it’ll depend upon what number of gutters your system connects to.

It additionally relies on the rainfall, season, and whether or not or not you’re experiencing a drought.

Both approach, in keeping with our calculations, it’s positively price it! You might both use the rainwater immediately or retailer it for later us.

Having correct storage will assist you to accumulate numerous water through the moist months. Then, you’ll have the ability to use that saved rainwater throughout dry months.

With the potential for gathering 19,099 gallons of water a 12 months, constructing a rainwater system is price it.



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