Rainwater Catchment Systems

Chuuk and Yap States, FSM

Is the tank you already have BIG Enough?

The steps that you should follow if you want to know if your OLD tank is BIG enough are exactly the same as you used to determine the size of a NEW tank except that you will also have to find out the number of gallons of water that your tank will hold. Here's the additional step:

• STEP 7.
  Find the SIZE of your tank (in gallons). See the sketch below for a description of the terms used.

Multiply 5.87 times height times diameter times diameter.

Tank Size = 5.87 x ________ x _________ x _________
Height Diameter Diameter

You will also have to use the charts in the back of the booklet in a slightly different way. This will be covered in example three which follows.

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EXAMPLE THREE

Your roof is 42 feet long and 47 feet wide. You have gutters around the entire roof but they leak a lot. There are 8 people in your home. Your tank is 9.5 feet in diameter and 6 feet high. Is your tank BIG enough for your family?

• Step 1.
  Length = ______feet
  Width = ______feet
• Step 2.
  s_____ x ______ = ______
  length width roof size
  
  Your answer should be 1,974 square feet.
• Step 3.
  s_______ roof factor
• Step 4.
  ________ gutter factor
• Step 5.
  ______x________ x ________ =________
  roof size roof factor gutter factor usable roof size
  
  Your answer should be approximately 1184 square feet.
• Step 6.
  ________people
• Step 7.
  5.87 x _______ x_______ x______ = _______ gallons
  height diameter diameter tank size
  
  Your answer should be approximately 3,179 gallons.
• Step 8.
  Now go to the chart for usable roof sizes between 1,000 and 1,200 square feet and look at the row for 8 people. Your tank is very close to the 3,100-gallon tank. So, let's look at the green boxes. The chart says that your tank is big enough for your family if you stop using the water in it for bathing and washing clothes when the level decreases below 1/2 full.

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EXAMPLE FOUR

Now suppose that you have a usable roof size of 500 square feet a 1,400-gallon tank and that there are 12 people in your household. Is your tank BIG enough?

Look at the chart for usable roof sizes between 400 and 600 square feet and the row of the chart corresponding to 12 people. Since red, the color corresponding to a 1,400-gallon tank, does not appear on the chart, your tank is too small. For your family, a 5,700-gallon tank (blue box) is required and the tank water must NEVER be used for bathing or washing clothes.

HAVING TROUBLE?

The author of this bulletin is hopeful that the procedures, charts and examples will help you in designing a new or evaluating an existing roof rainwater catchment system. If you are having trouble using the charts and examples or if your system does not seem to fit the charts provided, please contact your local sanitarian or contact Dr. Leroy Heitz at the address and numbers listed on the last page of this bulletin or e-mail directly lheitz(weri)uog.edu?subject=Chuuk and Yap States Tank Evaluation - WeriGuam.org.

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