The incident occurred in May 1997 following a major burst in a water main. North West Water had to shut off supplies to the area and re-zone properties to reconnect them to the supply. Change in pressures and flow patterns in the mains resulted in a few consumers nearby complaining of discoloured water.
However, the following day North West Water received about 100 complaints from customers in a more outlying area of the city. They described the water as "like mud", "sewagey", "brown" and "stagnant". Many found it unsuitable for drinking and washing, and analyses found that the supplies exceeded statutory limits for iron, manganese, aluminium and turbidity.
A prosecution was brought on the recommendation of the Drinking Water Inspectorate, and on 5 November the company appeared before Liverpool magistrates to answer two charges of supplying unfit water, contrary to section 70 of the Water Industry Act 1991.
The court heard that about 1,000 people may have been affected by the problem supplies, which were linked to a service reservoir. Investigations by the company revealed that internal baffles in the reservoir had been reported as being damaged or missing two years before the incident but had never been repaired.
The baffles served to distribute flows in the reservoir and prevent short circuiting between the inlet and outlet. The company conceded that the reduced retention time and an accumulation of stagnant water due to the absence of the baffles may have contributed to the water quality problems.
North West Water was fined £3,000 and ordered to pay prosecution costs of £2,842. The case was the company's first drinking water offence.