The Department of Health yesterday warned residents who live near the HWP fire to protect their water supply as thick smoke poured over the area.“Ideally all downpipes that connect the catchments and tanks should be blocked on houses immediately adjacent to the fire to prevent any pollutants that may have blown onto the roof from being washed into the water tanks by the next rainfall,” a Department spokeswoman said.“Furthermore, the catchment should be cleaned before being used to collect water again.”In order to seal the pipes, inflatable rubber stoppers, available at paint speciality stores, can be used.Another less expensive method involves wrapping a tennis ball in old cloth, covering it with a plastic bag, and using it to seal the downpipe.“Once the pollution episode is over, the entire roof surface should be thoroughly washed with clean water using a spray hose.‘Residents should then use a five gallon pail and a large sponge to remove the remaining water from the gutters, then unplug the downpipes.”