New Zealand's abundant rainfall feeds thousands of streams, over 70 major rivers, more than 770 lakes, and numerous under-ground aquifers containing cool groundwater or hot geothermal water. The rain also provides 75-80 percent of our electricity by feeding some 80 hydro power stations. The rainfall is not distributed evenly, however, because of the impacts of mountains on weather patterns. As a result, some parts of the country are prone to water shortages.
Droughts are common in 'rain shadow' areas of New Zealand, particularly along much of the east coast, and also in some inland and northern pockets of both the North and South Islands. Because many drought-prone areas tend to have high densities of livestock or people, dry spells can affect urban and rural water supplies and agricultural production. Hydro-electricity generation can also be affected.
Floods can occur in any season, and in all regions of New Zealand. The rate of flooding increased 50-150 years ago following widespread replacement of forests, scrub and tussock with shallow-rooted pasture grasses. Despite extensive river and catchment control schemes, damage from flooding is estimated to cost at least $125 million a year.
The main source of pressure on water is pastoralagriculture which has polluted many surface waters and some groundwater with sediment, animal waste and nutrients, and has also increased flooding and erosion in many areas by removing deep-rooted vegetation from hillsides and riverbanks. The use of irrigation water, mainly for pasture, is also a source of pressure on water levels in some South Island rivers and aquifers, as is land drainage for agriculture which has caused an 85 percent reduction in New Zealand wetlands.
In urban areas, pressures on water come from increasing consumption and from sewage and stormwater discharges. Additional pressures on water flows or quality come from the damming of rivers for electricity and water supply, the impacts of pests and weeds, and the potential impacts of climate change.
Pollution of rivers and coastal waters from point sources (i.e. specific sites such as dairy sheds, factories, sewer pipes) has declined over the last 20 to 30 years as treatment systems have been upgraded and alternative disposal methods are developed (e.g. onto land or into constructed wetlands).
Pollution from non-point sources (i.e. diffuse sites such as paddocks and roads) is still a major problem, particularly on pastoral and horticultural land where organic matter, nutrients, and sediment wash into waterways or nitrates leach into groundwater.
Urban stormwater causes serious problems in some areas (e.g. Auckland), polluting estuaries and harbours with sediment and toxic substances (e.g. heavy metals and hydrocarbons derived from motor vehicles) and, in some cases, infiltrating and flooding sewerage systems. Stormwater quality is often similar to that of secondary-treated sewage.
The natural character and habitat quality of many freshwater and estuarine waters has been lost or degraded by drainage, construction of flood control channels and stopbanks, development, removal of riparian vegetation, waste disposal, urban stormwater and agricultural run-off.
Invasive species of plants, fish and other animals pose a threat in freshwater ecosystems and in some parts of the coast where they have become established. Some of the toxic algal blooms which have recently become an intermittent problem in our coastal waters may involve exotic species introduced in ship ballast water.
Water quality is high in mountain streams and in sparsely developed areas throughout much of the South Island and the upper reaches of most North Island rivers. It declines measurably in lowland streams and rivers, particularly in pasture-dominated catchments. At times some lowland rivers are unsuitable for swimming because of faecal contamination from farm animals, poor water clarity, and nuisance algal growths. The stream water in some intensive dairy farming areas is in such poor condition that it may be unsafe for livestock to drink. The lower reaches of some rivers are also polluted by discharges of industrial wastes, urban sewage and stormwater run-off.
New Zealand's 30 or so large, deep lakes appear to be of high quality. However, more than 700 lakes are shallow and between 10 percent and 40 percent of these are nutrient enriched (eutrophic). Most of the eutrophic lakes are in the North Island and in pasture-dominated catchments. A number are subject to fish kills or are no longer capable of supporting fish life.
The state of our groundwater is largely unknown. However, many shallow aquifers beneath dairying or horticultural land have elevated nitrate levels. The extent of contamination from seepage from landfills, other waste disposal systems, and contaminated sites is unknown. The extent of pesticide contamination in groundwater is also largely unknown. The few surveys to date have found pesticide traces, but at very low concentrations. In some coastal areas, seawater has contaminated groundwater after excessive use during dry seasons has reduced the groundwater level below sea level.
New Zealand has 1,638 community drinking water supplies and these serve 85 percent of the population. Of these, 7 percent (serving 54 percent of the population) are considered safe, while a further 2 percent (serving 5 percent of the population) are of borderline safety. However, 19 percent (serving 18 percent of the population) have an unsatisfactorily high risk of contamination. The remaining 71 percent of water supplies (serving 8 percent of the population) have not been graded because they are in communities of less than 500 people. Approximately 15 percent of the population are not connected to community supplies.
Many geothermal phenomena (e.g. geysers, hot springs, mud pools) have been affected by human activities. Between 1950 and 1990 the number of active geysers declined from 130 to 11 as a result of flooding for hydro dam construction, the draw-off (or abstraction) of steam for geothermally-powered electricity production, and the draw-off of hot water for household and commercial use. No geothermal fields are formally protected from abstraction, and no dormant geysers have been able to be restored.
Wetland areas have been reduced by about 85 percent in the last century and a half, from nearly 700,000 hectares to about 100,000 hectares. Several thousand wetlands remain, including more than 70 which are deemed to be of international importance. Many of the surviving wetlands have been degraded by drainage, pollution, animal grazing and introduced plants.
From the limited data available, the state of our sea water seems generally good, except near some river mouths and in some harbours and estuaries where sediment, heavy metals, nutrients, bacterial counts and marine debris levels have been elevated by urban stormwater, sewage and agricultural run-off. In addition, at least 100 oil spills occur each year in the major harbours.
Sediment from rivers is a serious threat to some coastal ecosystems, particularly estuaries. Marine debris (particularly plastic wrapping and containers) is a significant health threat to marine mammals and seabirds and is associated with increasing population size in coastal areas. Waste from fishing and recreational boats has the potential to cause localised problems. Another threat comes from toxic algal blooms which occasionally irrupt in coastal waters.
Management of natural water (i.e. freshwater, groundwater, geothermal water and coastal water) is the responsibility of Regional Councils which, under the Resource Management Act, are required to safeguard the life-supporting capacity of waters and ecosystems and ensure that water users avoid, remedy, or mitigate any adverse effects of their use on the environment. Council approval is required for abstracting, damming or diverting water, discharging pollutants into it, or placing structures on the beds of lakes, rivers and the coast. These approvals, and the environmental limits on use (e.g. water quality standards), are issued through policy statements, plans and water permits.
Regional Councils are responsible for monitoring the environmental impacts of the water uses for which they have issued permits (consent monitoring) as well as broader monitoring of water and other resources (environmental monitoring). In addition to these planning and regulatory roles, Councils also have responsibility for flood control, civil defence and dealing with oil spills out to the territorial sea limit.
Central government also has responsibilities for improved water management, including:
the 1986 National Wetlands Policy (Minister of Conservation);
the nation's coastal policy (Minister of Conservation);
managing water bodies on Conservation Department land (Department of Conservation);
approving Water Conservation Orders (Minister for the Environment);
producing water quality guidelines and standards (Ministries of Health and Environment);
monitoring drinking water supplies (Ministry of Health);
monitoring toxic algae in coastal waters (Ministries of Health and Agriculture);
funding research and development to improve water and soil management (Foundation for Research, Science and Technology, Ministry for the Environment, Ministry of Agriculture); and
safeguarding the Crown's property interests in freshwater fisheries and their habitats (Department of Conservation).
Responses by industry and land user groups include the development of codes of practice (e.g. by the Forest Owners' Association), the development of farmers' landcare groups, and the adoption of improved forms of waste water disposal by farms and factories (e.g. constructed wetlands).
Most information on the state of our water resources is collected for local use by regional councils and by territorial authorities involved with water supply and disposal. Some data are also collected, or collated from local authority collections, by Crown Research Institutes. Because the data are primarily for local authority use, the monitoring methods, and the parameters and indicators measured, may differ from one authority to the next. This makes it difficult to combine the data across regions to provide a national picture of the state of our water.
Water management and monitoring will become easier as information systems become better integrated and standardised. A key part of this is the development of a core set of water quality indicators and an agreed methodology and programme for monitoring and updating them.