Introduction

Questions of tap water being safe to drink are usually prompted by sensational media articles or scare tactics and ambiguous statements of the seller of bottled water or home water treatment devices. They often mislead customers into purchasing expensive treatment systems for supposed health reasons. The truth is that devices are completely unnecessary in Johannesburg as the tap water is perfectly safe to drink.

Some of these traders are prompting sales of home treatment systems and bottled water by demonstrating a colour change in our tap water which then does not occur in their bottled water. The demonstration unit comprises two clear bottles, one containing tap water and the other the bottled water. Two electrodes are then placed in each bottle. In each case one electrode is made of iron and the other aluminium. These electrodes are then connected to an electrical power source.

As the tap water contains a certain amount of dissolved salts it is able to conduct an electrical current when the power is turned on. This causes one of the two electrodes to dissolve in the water resulting in colour change and formation of visible particles. As the bottled or treated water they use in this experiment contains very low concentrations of dissolved salts, it cannot conduct the current, therefore no colour or particles are formed.