Rehabilitating small-scale piped water distribution systems
Technical note 4 on drinking-water, sanitation and hygiene in emergencies
Step 6: Test, clean and disinfect the repaired pipe sections
Partly open the upstream isolation valve and the downstream washout to fill the repaired pipeline section with water. Once full, increase the pressure in the pipe by at least 50 percent. This is achieved by:
- closing the upstream valve and downstream washout;
- connecting a water pump between a water tanker and the upstream fire hydrant; and
- switching on the water pump and maintaining the high pressure for at least 4 hours.
Observe the pipe joints for leaks and repair if necessary. Check the amount of water being pumped from the tanker into the pipeline and compare with the figures given in Table 4.1. If the leakage is greater than recommended, it indicates other major leaks in the section. Sources of further information about ways of searching for hidden leaks are provided below.
Connect a full tanker of clean water, via a water pump, to the upstream fire hydrant or washout for the section of pipe you are working on. Confirm the pump can deliver the quantity of water and pressure required to flush and clean the pipe. Table 4.2 gives guidelines for adequate velocities and flow.
Open the hydrant connected to the pump and tanker. Turn on the pump. Gradually open the downstream washout valve until the flow rate reaches the required level. Pump until the water coming out of the washout is completely clean but not less than the time suggested in Table 4.2.
Direct flushing water away from traffic, pedestrians and private plots. Avoid erosion damage to streets, lawns and yards by use of tarpaulins and lead-off discharge devices. Avoid flooding which can cause traffic congestion. When the water coming out of the pipe is clean, slowly close the washout valve before turning off the water pump.
Calculate the volume of water required to fill the section of pipe using Table 4.3. Acquire tankers of volume equal to, or higher than, the calculated volume of the pipe. As the tankers are being filled with clean water add 80g of High Strength Calcium Hypochlorite (HSCH) granules for every 1000 litres (See Technical note 3 for further information about the chlorination of tankers).
Connect the water tanker to the up stream fire hydrant. Open the valves between the tanker and the pipe. Gradually open the down stream washout so that the chlorinated water replaces the clean water in the pipe (it may be necessary to pump water into the pipe).
Continue feeding water into the pipeline until chlorine can be strongly smelt in the water coming out of the washout. Close the washout valve but leave the inlet valves open so that chlorinated water can still enter to replace leakage. Leave the pipeline for 24 hours.
Disconnect the water tanker and open the upstream isolating valve. Gradually open the downstream washout and monitor the water coming out until it no longer smells strongly of chlorine. The pipe can then be returned to service.