On an international scale, New Zealand has an abundance of fresh water. However, demand for water per capita is high and is growing. New Zealand’s water supply is not evenly distributed, and resource limits are being reached in some parts of the country. This can result in the loss of in-stream values, poor water quality, water shortages and water-constrained economic opportunities.
In 2017, more than half of the water allocated or consented by councils is for irrigation, 14% for drinking water, 13% for industry and 22% for other purposes 5038 Not all the water is used and we don't know exactly how much of it is used. From 2016, water users will have to provides a record of water they take each year. 5039
Water that is taken from groundwater reserves can be replaced by rainwater, but if too much is taken, the level of water in the aquifer can permanently decrease. This is known as lowering the water table. Where the water table is permanently lowered, this may have effects on surrounding streams and wetlands, as many may rely on groundwater flow particularly in the dry season when there is not enough surface water available to support them. Land may subside and in coastal areas, salt water may infiltrate fresh water as the water table drops. In addition, users with shallower wells may lose their supply.
Abstraction of large amounts of water from a water body can have significant effects on its ecological health. When large amounts of water are removed from a river, not only does the level of flow decrease, but the natural variability of the flow may also be affected. These changes can destroy the river’s natural character, as the varying flow is part of what has caused the river to develop the characteristics that it has. Unusually high flood flows that occur during periods of heavy rain can be important for keeping the river downstream clean, reducing nuisance plant growth, clearing away weeds and helping maintain its braided nature.
Reducing flow variability and flow levels can impact on fish, invertebrates and bird life. It can also affect the recreational values of a river. For example, kayakers and boaters require a minimum water level in order to undertake their activity.
Some rivers are particularly susceptible to damage from abstraction. Decreasing the flow in a braided river may eliminate some side braids altogether, as the reduced flow cannot sustain more than the main channel. This results in a decline in available habitat for braided river species – for example the dwarf galaxias, a rare native fish, tends to live in these side braids. Many invertebrates live there and they can be an ideal foraging habitat for birds such as the rare black fronted tern.
Dams are often used to store water for abstraction. Their construction in a previously natural environment can have serious adverse environmental effects. Dams do not just prevent water from moving down a river, but also gravel and silt that would normally be carried along by the water. Sediment that would naturally be transferred downstream can thus build up behind the dam. This can exacerbate downstream and coastal erosion as gravel and silt that would normally replace eroded areas is not available. Erosion of the river bed and riparian areas results in the loss of habitat for many species, for example native fish that normally inhabit the crevasses between pebbles on the river bed. In addition, dam structures can prevent fish passage along the water body. This problem can be mitigated if effective fish passes are used to allow the fish through the structure.
Abstraction of geothermal fluid for energy generation can result in a reduction in the temperature and pressure in geothermal fields. This in turn can lead to a loss of geothermal features such as geysers as well as result in ground subsidence.
page 12, Ministry for the Environment (2017) Our Freshwater 2017
Last updated at 2:18PM on April 3, 2018