By
Dr. Leroy F. Heitz

Water and Environmental Research Institute of The Western Pacific

University of Guam

These guidelines should only be used for:
Pohnpei Island, and Ant, Ngetik, Mwokil and Pingelap Atolls in Pohnpei State, FSM

Introduction

This booklet provides answers to THREE QUESTIONS:

• How BIG should you make a NEW rainwater storage tank?
• Is your OLD rainwater storage tank BIG enough?
• What should the water in your storage tank be USED FOR?

In the home, the SIX MAIN USES OF WATER are:

• Drinking
• Cooking
• Washing dishes
• Bathing
• Washing clothes
• Flushing toilets

Here are some RULES:

• ALWAYS use the water in your rainwater storage tank for drinking, cooking, and washing dishes.
• SOMETIMES use the water in your rainwater storage tank for bathing and washing clothes.
• NEVER use the water in your rainwater storage tank for flushing a toilet.

So, we have almost answered the question "What should the water in your rainwater storage tank be used for?" We only have to find out WHEN it should or should not be used for bathing and washing clothes. This booklet will give you the answer to this question.

BASIC ASSUMPTIONS

All of the information given in this booklet is based on some ASSUMPTIONS. They are:

• Your home uses around 4 GALLONS of water per person per day for drinking, cooking, and washing dishes.
• Your home uses around 11 GALLONS of water per person per day for bathing and washing clothes.

If you use less than this, the tank sizes given in this booklet may be larger than necessary. If you use more than this, they may be too small.

The information provided in this booklet is applicable to Pohnpei Island and Ant, Ngetik, Mwokil and Pingelap Atolls. The design criteria provided is based on rainfall at the Pohnpei Island US Weather Service Gage. It is recognized that there are some differences between the rainfall at the Pohnpei gage and the rainfall on the atolls listed. It has been determined that the difference is small enough to be insignificant for the uses made in this booklet.

If you live somewhere other than the areas specified above, you should not depend on the charts provided in this booklet.

Since you can not use your rainwater storage tank for bathing and washing clothes all the time, it is important to have access to another dependable source of water. A well or stream is the most common source. If you do not have access to such a source, you will be tempted to use your tank for purposes other than those that are recommended in this booklet. If you do this, YOUR TANK MAY BECOME EMPTY.

CHARTS FOR TANK SIZING

The charts in the back of this booklet are based on COMMON FERROCEMENT TANK SIZES. All are 6 feet high. Their diameters depend on the number of pieces of standard reinforcing rod (rebar) that is used to go around their circumference. Here is a summary of the important information about these tanks:

The charts also refer to a 500-gallon tank. This is a popular size of fiberglass or plastic tank.

If you feel that the information given in this booklet does not answer questions you have concerning the design of your rainwater catchment and storage system, please contact the Water and Environmental Research Institute (WERI) for further information. The mailing and
e-mail addresses and telephone and fax numbers for WERI are provided at the end of this booklet. You can also send e-mail to Dr. Heitz via lheitz@uog.edu.

SIZING NEW TANKS

Here are the STEPS to use if you want to know how BIG to make a NEW tank:

STEP 1.
Measure the LENGTH and WIDTH of your roof.

STEP 2.
Find your ROOF SIZE.
Multiply Length times Width.
Roof Size = Length x Width

STEP 3.
Select a ROOF FACTOR.

If the entire roof has gutters, use 1.0
If 3/4 of the roof has gutters, use 0.75
If 1/2 of the roof has gutters, use 0.50
If 1/4 of the roof has gutters, use 0.25

STEP 4.
Select a GUTTER FACTOR.

If your gutter has only a few leaks, use 0.90
If your gutter has a number of leaks, use 0.75
If your gutter has a lot of leaks, use 0.60

STEP 5.
Find your USEABLE ROOF SIZE.
Multiply Roof Size times Roof Factor times Gutter Factor.
Usable Roof Size = Roof Size x Roof Factor x Gutter Factor

STEP 6.
Write down the NUMBER OF PEOPLE that live in your home.

STEP 7.
Use the CHARTS at the back of this booklet to get the size of your NEW tank. Click here to view these charts