Water Quality & Standards

The level of treatment that is required to meet the New Zealand Drinking Water Quality Assurance Rules is dependent on the quality and consistency of the source water.

All supplies need to be chlorinated to treat bacteria. The requirements to treat protozoa are more complex. This typically requires some form of filtration, and ultraviolet (UV). Membrane filters are one type of filter that do not require UV, but these are significantly more expensive to construct and operate.

Surface water sources require more treatment processes to treat protozoa than groundwater sources. This is because surface water has more risks associated with it, and typically has less consistent quality than ground water. The more treatment processes, and the higher the level of filtration required, the higher the cost it is to construct and operate.

Source water that is affected by turbidity is more difficult to treat. Turbidity is when there is sediment in the water, which is usually caused by rain causing runoff into the streams and rivers. When rivers and lakes are dirty due to sediment, this impacts on the ability of some treatment processes to work effectively.

For these reasons investigation is required to identify the different source water options that are available. Testing of the best option is then needed over at least a 12-month period to identify how consistent the quality and quantity of the water is. This is to ensure that the treatment plant built can treat the source water under all conditions.

There are different requirements in the New Zealand Drinking Water Quality Assurance Rules for water supplies that serve more than 500 people, 100 to 500 people and less than 100 people.