Math CentralQuandaries & Queries


Question from shannon, a student:

I'm doing a report to reclaim water off of our campus facility to store in a cistern to use to flush toilets.

In Southeast Wisconsin and average of 82 inches of rain and snow fall annually.
I want to collect that off of the roof of our school building.
The roof is 37128 square feet.
how many gallons annually could I collect?

Hi Shannon,

There are 7.4805 US gallons in a cubic foot so if you calculate the volume in cubic feet you can convert it to gallons. First convert the depth of 82 inches to feet and then multiply by the area of the roof in square feet to calculate the volume in cubic feet.

Of course it isn't that easy, the amount of water you can collect depends on other factors as well. For example, how much do you lose in evaporation? Can you melt the snow and collect the water? Snow is likely to sublimate rather than melt.


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