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Twenty tonnes of aluminium sulphate were tipped into the wrong tank at a treatment works on 6 July 1988, contaminating water to 20,000 homes.

The water was poisoned when a relief delivery driver mistakenly tipped 20 tonnes of aluminium sulphate into the wrong tank at Lowermoor water treatment works.

His findings dictate how much aluminium sulphate must be added.

Using a system of pipes and pumps, water is drawn from the river into floatation tanks, where aluminium sulphate is added to remove the sediment.

Aluminium sulphate was released into the river from the Glenfarg Water Treatment Works overnight.