By world standards New Zealand has high-quality water available for many uses. A plentiful supply is something that New Zealanders have taken for granted since the days of early settlement. Maintaining the quality has, for a long time, been largely due to the low population and the low level of contaminants from farming and urban development.
How we use water
People have contact with water in many ways, including:
- wading in streams and rivers while tramping or fishing
- boating, swimming or fishing in lakes
- washing or drinking from a reservoir or water tank.
Other uses include:
- farm irrigation and drinking water for animals
- effluent disposal
- generation of hydroelectricity
- as a coolant for thermal power stations.
What is ‘clean’ water ?
Water quality must be defined according to different uses. Water that is unsuitable for drinking is still usable for washing or many other purposes. In the case of freshwater species, eels tolerate high water temperature, oxygen depletion and low water clarity, whereas trout need a lower temperature, a high level of dissolved oxygen, and clear water.
Washing or wasting?
New Zealanders use about 560 cubic metres of water each per year: that’s 1.5 cubic metres down the drain every day. The United Kingdom is less splash-happy, with 230 cubic metres per person per year. Canadians use a whopping 1,420 cubic metres.
In the early days of settlement, when forests were being converted to pasture, some hill country regions, especially in the North Island, suffered severe soil erosion. This smothered natural waterways and contributed large quantities of sand, silt and clay to rivers, estuaries and coastal regions. Through the early and mid-20th century, eroded soil was the main contaminant affecting rivers and lakes.
Sewage and other pollution
Until the late 1970s the discharge of sewage to waterways caused environmental and health problems. Organic wastes (from meat works, milk factories, wood pulp mills) depleted oxygen in a number of rivers and lakes. These practices are now unacceptable, and most effluents are treated before being discharged into waterways, irrigated onto land, or released into the ocean. As a result, pollution from these sources is now rare, and usually accidental.
Too much of a good thing
In the right place, chemicals such as phosphorus and nitrogen in farm fertiliser are good – nutrients for crops. But when these chemicals are washed into waterways, they upset the natural balance of the water. Also, added chemicals make water weeds grow rapidly and use up oxygen. This can affect fish, lower water quality and clarity, and smother river beds.
By 2000, concern for water quality had shifted its focus from pipes and drains to reducing the impact of more diffuse sources on small streams and groundwater, and the cumulative effect on larger rivers, lakes and estuaries. There have been marked increases in dairy, cattle and deer numbers (but decreased sheep numbers), fertiliser use, animal stocking rates, productivity per hectare, and cropping. These have contributed to the raised levels of nitrate, phosphate, sediment and pathogens in waterways.