Backflow Incident - Melbourne

An incident occurred at a Melbourne Service Station, where car wash waste water and sewer was drawn into the internal potable water supply system.

Due to a blockage in the sewerage system, sewer backed up and filled a car wash below ground recirculation tank. At the same time the water supply had been turned off at the meter -apparently as a prank.

Arriving on a Saturday morning with an anticipated rush of car wash customers, the service station attendant immediately opened the car wash and turned on the pumps.
As usual, the pumps were started by priming with water from the mains supply.
With some difficulty in priming the pumps, the operator left the supply on, and opened other areas for business.

With the arrival of cars to the car wash, the pumps appeared to be operating and so business continued throughout the morning. At the same time there was water at the tap outlets, and there was no indication that the main supply had been turned off.

At around lunchtime, a customer complained that the water from a tap at the petrol filling area had a “funny smell and taste”. The attendant was busy, but a few more complaints from customers raised the attendants concerns, who then checked the problem and called a plumber. The plumber resolved the problem on Saturday evening by turning on the water at the meter, unblocking the drains and fitting a check valve to the pump priming line.

It appears that throughout Saturday, there was enough waste water to run the car wash and, pump waste water back through the potable water supply system. Of course water for flushing toilets was being recycled, entering the drainage system, recirculation tanks and back into the potable supply lines.
Equipment connected to the potable water supply system included taps at petrol filling areas which could have been used to fill customers drink containers, a coffee machine and flavoured ice machine.