John Oliver, of Mokoia Intermediate School, asks :-

Is water a neutral, acidic or alkaline?

Tim Charleson, a water chemist with the Rotorua District Council, responded.

To answer this question it may help to explain what these words mean. A term used which indicates whether water is acid or alkaline is pH. The pH value can range from 0 to 14 and is a measure of things called acid ions in the water.

A pH of less than 1 indicates the water is very acidic (lots of acid ions) and a pH of 14 very alkaline (very few acid ions) and both would damage your skin at these pH levels!

Water that is neutral (pure water) has a pH of 7 which is the middle of the pH scale. Above pH 7 it is called alkaline and below 7, acid. To help appreciate the pH values of things we know and use look at the list below: Solution pH value Stomach acid 1.0 Lemon juice 2.3 Milk 6.6 Pure water 7.0 Blood 7.4 Toothpaste 9.9 Household ammonia 11.9

Water found naturally in the environment can be acid or alkaline but more commonly in New Zealand it is slightly acid. Water is safe to drink in the pH range 6.5 to 8.5 and as can be seen in the above list, a pH in the range 2.5 to 9 is unlikely to cause harm solely due to pH. Water in rivers that are polluted will be acid or alkaline often depending on the pH of pollutants going into the river.

Rain water is also slightly acid and in industrial countries where there is a lot of air pollution the rain can be very acid (below 6) and this is called "acid rain". This rain cause the rivers and lakes to become acid and is damaging to the environment.

Acid waters tend to corrode metal pipes and consequently many Councils as part of their water treatment will add chemicals to make sure the water is slightly alkaline (about pH 7.5) to protect all the metal pipe work including that in all the households.