Water is essential to New Zealand’s social, cultural, and economic well-being. It is also a focal point for recreational activities and our outdoor-focused way of life. New Zealand has 425,000 kilometres of rivers and streams, almost 4,000 lakes that are larger than 1 hectare, and about 200 aquifers.
By international standards, freshwater in New Zealand is both clean and plentiful in supply. However, demand for water is increasing. At the same time, some aspects of water quality are getting worse in areas that are dominated by intensive land use.
Rivers in catchments that have little or no farming or urban development make up about half of the total length of New Zealand’s rivers and have good water quality. Water quality is generally poorest in rivers and streams in urban and farmed catchments. This reflects the impact of non-point-sources of pollution in these catchments, that is, pollution that does not have a single identified point of origin, such as urban stormwater, animal effluent, or fertiliser run-off. The proportion of the total river length that is in farmed catchments is more than 40 times the proportion that is in urban catchments.
While the levels of nutrients (which, in excessive amounts, reduce water quality) in our most polluted rivers are only about half the average for all rivers reported by countries to the Organisation for Economic Co-operation and Development (OECD), nitrogen and phosphorus levels have increased over the past two decades. Nitrogen levels have increased most rapidly in rivers that are already nutrient-enriched.
Pollution from organic waste in rivers has reduced since the late 1980s. This indicates improved management of point-source discharges of organic waste, that is, pollution from a single facility at a known location, such as discharges from wastewater treatment plants, meatworks, and farm effluent ponds.
Two-thirds of New Zealand’s lakes are in natural or partially developed catchments, such as native bush, and are likely to have good to excellent water quality. Small, shallow lakes surrounded by farmland have the poorest water quality of all our lakes.
Over the 2006–2007 summer, 60 per cent of the swimming spots on rivers and lakes that were monitored had low levels of bacteria, indicating that these sites have good water quality and are suitable for swimming. Ten per cent of the monitored swimming spots frequently had levels of high bacteria, indicating that they are generally unsuitable for swimming. Bacteria levels appear to have improved in our recreational waters over the past few years.
Sixty-one per cent of the groundwaters in New Zealand that are monitored have normal nitrate levels; the remainder have nitrate levels that are higher than the natural background levels, and 5 per cent have nitrate levels that make the water unsafe for infants to drink. Twenty per cent of monitored groundwaters have bacteria levels that make the water unsafe to drink. High levels of nitrates and bacteria are particularly common in shallow, unconfined aquifers. These aquifers are the most vulnerable to pollution from land-use activities, such as farming and urban development.
Because New Zealand has a low population and high average rainfall, it has more total freshwater per person than more than 90 per cent of almost 200 other countries around the world. However, not all of this water is in the right place at the right time; some areas experience a surplus or shortage of water.
It is estimated that total water use in New Zealand currently equates to two to three times more water per person than in most other OECD countries. Demand for water is increasing, particularly in areas that are already short of water. Drier parts of the country have the highest demand. For example, Canterbury accounts for over half of all water allocated in New Zealand; that is, the amount of water that is permitted to be used. Several eastern regions, including Canterbury and Ōtago, have surface water catchments that are highly allocated, so come under pressure during drier times of the year.
The allocation of water in New Zealand increased by 50 per cent between 1999 and 2006. This is mainly a result of an increase in the area of irrigated land. Irrigation now uses almost 80 per cent of all water allocated.
Because pollution of freshwater from point-source discharges is now largely controlled under the Resource Management Act 1991, attention of resource managers has turned to reducing non-point-source pollution from intensive land use. As a result, there is greater emphasis than in the past on managing intensively used land through stream-bank (riparian) planting, nutrient management, and excluding stock from waterways using bridging and fencing.
Water allocation and pollution caused by intensive rural and urban land use will continue to be the focus of freshwater management in New Zealand. Balancing the competing needs of water users – recreational users, town water suppliers, hydro-electricity generators, tourist operators, and farmers – is likely to become increasingly important.