Proper Cistern Care:
Cisterns, if not taken care of, can be contaminated with bacteria, viruses, hydrocarbons from leaking
fuel tanks, pesticides from farms, fecal Coliform from septic tanks, dirt, leaves, plant toxins, just
about anything that can wash off the roof or seep in from the ground!
The first step is to take care that debris does not enter the cistern by keeping downspouts screened
and cleaned and keeping the catchment area (roof) as clean as possible. Cisterns need to be cleaned
periodically to remove the muck that builds up on the bottom.
The next step is to chlorinate the cistern water. Use plain old liquid bleach from the supermarket.
See the table below for the recommended amount of bleach to put in the cistern. Chlorinate monthly
or when there is a heavy rain. Ocean Systems sells appropriate kits for $45.00.
How much water is in your cistern?
Measure the length and width of the cistern. Then measure the depth of your water using a stick.
Multiply the length times the width times the depth to obtain the number of cubic feet.
Multiply that number by 7.67 to determine the number of gallons of water in the cistern.
L x W x D = Cubic Feet x 7.67 = Gallons of water in the cistern
Use Caution with Chlorine!
Drinking chlorinated water can be hazardous to your health as chlorine reacts with the organic material
washed into the cistern from the roof causing the formation of tri-halomethanes. To get rid of the
contaminants formed from the addition of chlorine a charcoal filter is needed.
A word of caution: If the chlorine is not kept up, the bacteria will thrive and go right through the
charcoal filter. So be wise, monitor the chlorine and keep it up. Also change the charcoal filter
regularly. We recommend monthly filter changes with cisterns.
The safest cistern treatment to use is an ultraviolet system.
Read about ultraviolet water treatment
Please note: This is an external link off our site for educational purposes only. No endorsement is implied.
How Much Chlorine to Use?
Use only regular household bleach that contains 5.25% sodium hypochlorite. Do not use scented bleaches,
colorsafe bleaches or bleaches that have added cleaners. Measure using cups or ounces below.
GALLONS OF
CISTERN WATER | | CUPS | | OUNCES |
| 1,000 | | 4/5 | | 6 |
| 5,000 | | 3 3/4 | | 30 |
| 10,000 | | 7 1/2 | | 60 |
| 15,000 | | 11 1/4 | | 90 |
| 20,000 | | 15 | | 120 |
| 25,000 | | 18 3/4 | | 150 |
| 30,000 | | 22 1/2 | | 180 |
| 40,000 | | 30 | | 240 |
Useful Links:
EPA Beaches Website
Local Beach Monitoring
