4 Apr 11 10:34
Here is a specification for the test:
A. Upon completion, the tank shall be tested to determine watertightness. The tank shall be filled with potable water to the maximum level.
The test shall consist of measuring the liquid level over the next 24 hours to determine if any change has occurred. If a change is observed and exceeds the maximum allowance, the test shall be extended to a total of five days. If at the end of five days the average daily change has not exceeded the maximum allowance, the test shall be considered satisfactory.
B. The liquid volume loss for a period of 24 hours shall not exceed one-twentieth of one percent of the tank capacity, 0.0005 x tank volume. If the liquid volume loss exceeds this amount, it shall be considered excessive, and the tank shall be repaired and retested.
C. Damp spots will not be permitted at any location on the tank wall. Damp spots are defined as spots where moisture can be picked up on a dry hand. All such areas shall be repaired as necessary.
D. Damp spots or standing water on the footing may occur upon tank filling and are permissible within the allowable volume loss. Measurable flow in this area is not permissible and must be corrected.
Per AWWA, the allowable leakage rate is 0.1 percent of the water volume in 24 hour.
You can always specify higher requirements than the minimum standards.
This issue was previously discussed:http://www.eng-tips.com/viewthread.cfm?qid=222702&page=15