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Topic 4: Water

Water in rivers, lakes, and wetlands, and the marine environment are important resources for New Zealand. Good quality water is valued for many reasons, including its ecological function and role in maintaining biodiversity, its recreational value, its role in supporting industry, and its cultural significance. It is used for drinking, irrigation, many industrial processes, and for absorbing pollutants.

As a renewable natural resource, it is necessary to ensure that water resources are not depleted in quality or quantity over the long term. An adequate amount of clean water is required to meet basic needs. Water is also particularly important for economic development in New Zealand where agriculture is a significant part of the economy. This topic reports on fresh water and the recreational aspect of the marine environment.

Main results

Between 2001 and 2008, the proportion of the population with access to water that meets drinking-water standards has increased.

Since 1989, an increasing trend for the level of nitrogen in rivers and streams has been recorded, indicating increased levels of pollution. However, the biological health of rivers has shown little change since 1996, with the majority of monitored sites in 2007 recording good to excellent water quality.

Between 1990 and 2006 there was no clear overall national trend for water quality in lakes in New Zealand. Similarly, between 1995 and 2006, there was no clear national trend in groundwater nitrate levels. It was not possible to make a trend assessment for water quality at swimming spots as the time series is not long enough to assess whether improvements are a result of human factors or annual weather variations.

The total amount of water allocated in New Zealand increased by 50 percent between 1999 and 2006. In 2006, water stress (allocation relative to available water) was low in all regions, except Canterbury.

Table 4.1
Water indicators – key results

 Water indicators - key results.

What the indicators tell us

Population with drinking water meeting standards (indicator 4.1)

An increase in the proportion of the population with access to good quality drinking water ensures that less of the population is at risk of water-borne disease. The quality of drinking water is measured against standards for acceptable levels of contamination by living organisms and chemicals.

Between 2001 and 2008, the proportion of the population with access to drinking water that met acceptable bacterial standards increased from 63 percent to 83 percent. Over the same period, the percentage that met standards for protozoa (parasites) increased from 52 percent to 67 percent (see figure 4a).

Information on the percentage of the population with access to drinking water that meets chemical standards is available from 2003. Between 2003 and 2008, this increased from 78 percent to 92 percent (see figure 4a).

 Proportion of population with drinking water supply meeting standards, by water standard type.

Nitrogen in rivers and streams (indicator 4.2)

Nutrients, such as nitrogen and phosphorus, occur naturally in fresh water and are needed by aquatic plants for growth. However, increased levels of nutrients caused by human activity can unbalance water ecosystems and result in excessive plant growth and algae blooms. In urban rivers and streams the main source of introduced nutrients is sewage, while the main sources in rural areas are run-off of agricultural fertilisers, and stock manure and urine.

This indicator measures levels of total nitrogen in river reaches in New Zealand.

Between 1989 and 2007, the median level of nitrogen in monitored rivers increased by 4.6 percent. This is based on an average increase of 1.4 percent per year. Figure 4b shows changes in nitrogen levels for rivers with the lowest (5th percentile), median, and highest (95th percentile) nitrogen concentrations. Nitrogen levels are increasing fastest in rivers which already have high levels of nitrogen.

Between 1989 and 2007, the level of total phosphorus in rivers increased on average by 0.53 percent per year, although the median levels have fluctuated. However, for rivers with a high level of phosphorus (in the 95th percentile) the levels have decreased over the period.

 Nitrogen concentrations in rivers, by percentile group, 1989–2007.

Biological health of rivers and streams (indicator 4.3)

The macroinvertebrate community index (MCI) provides a single number that summarises the pollution sensitivity of the macroinvertebrate community at a site.

Freshwater macroinvertebrates are small aquatic animals such as insects, worms, and snails. Their presence is affected by changes caused by human activity, as well as natural events such as floods and droughts. The abundance of these creatures, both in number and species type, is an indicator of overall stream health and water quality over time.

An MCI of less than 80 indicates poor water quality and an MCI greater than 119 indicates excellent water quality. Between 2005 and 2007, the average MCI across 66 monitored sites was 109. Good to excellent water quality was recorded at 51 of the sites (77 percent) and three of the sites had poor water quality.

The median MCI of monitored sites has fluctuated, but decreased 7.8 percent between 1996 and 2007. For sites with the lowest water quality, as indicated by MCI (in the 5th percentile), the MCI increased over the same period (see figure 4c).

 Macroinvertebrate community index (MCI) in rivers, by percentile group, 1996–2007.

Lake water quality (indicator 4.4)

New Zealand has 3,820 lakes that are over one hectare in size, and many more smaller ones. This indicator measures changes in the nutrient levels of 49 lakes for which long-term monitoring exists.

In lakes with high levels of nutrients, algal blooms are common, water clarity is reduced, and the health of aquatic animals is at risk. High nutrient levels impact on natural ecosystems and the recreational use of lakes. The nutrient levels of lakes are affected by natural factors such as lake depth, air temperature, and wind, as well as human land use in the lake’s catchment area.

Between 1990 and 2006, there was no clear national trend for water quality in lakes. The nutrient level in 33 of the 49 monitored lakes showed no signs of change over this period. Possible or definite signs of deterioration, such as increased nutrient or algae levels, or decreased visual clarity, occurred at 10 lake sites, of which 9 were already nutrient-enriched. Six of the 49 lakes showed signs of improvement over the period (see figure 4d).

 Trends in lake water quality, December 1990–2006.

Groundwater quality (indicator 4.5)

This indicator measures levels of nitrates in water beneath the ground’s surface. The quality of groundwater affects health, as a source of drinking water (see indicator 4.1), and water quality in rivers and lakes, and in freshwater ecosystems (see indicators 4.2 and 4.4). Groundwater drains into rivers and lakes, and therefore high nitrate levels in groundwater can increase nutrients, such as nitrogen and phosphorus, in rivers and lakes.

Increased levels of nitrate are caused by the by-products of human activities, such as wastewater (sewage), agricultural fertilisers, and stock effluent. Nitrate can be a good indicator of general groundwater degradation as increased levels often indicate the presence of other pollutants, such as faecal pathogens and pesticides, from human activities.

Between 1995 and 2006 there was no clear national trend in groundwater nitrate levels; 13.1 percent of sites showed a significant increasing trend in nitrate levels, and 11 percent had a decreasing trend (see figure 4e).

Based on the median for each site over the period 1995 to 2006, 39 percent of sites had levels of nitrate that were higher than natural levels, 4.9 percent had nitrate concentrations exceeding the drinking water standard, and 10.3 percent exceeded the trigger level for ecosystem protection (Ministry for the Environment, 2007b).

 Trends in groundwater nitrate concentrations, December 1995–2006.

Bacterial pollution at coastal swimming spots, rivers, and lakes (indicator 4.6)

Swimming is one of many recreational activities dependent on clean water for its intrinsic enjoyment. This indicator measures the proportion of monitored coastal and freshwater swimming spots that meet New Zealand’s guidelines for recreational water quality.

In the summer of 2006/07, the proportion of river and lake sites that met the guidelines almost all the time was 60 percent. This was an improvement on 41 percent in 2003/04. In 2006/07, 10 percent of sites breached the guidelines regularly.

In 2006/07, the proportion of coastal sites that met guidelines almost all the time was 80 percent, an improvement on 65 percent in 2003/04 (see figure 4f). In 2006/07, only 1 percent of beaches breached guidelines regularly. Coastal swimming spots show better compliance than freshwater sites because pollutants are more rapidly diluted and dispersed in the sea, by currents and large volumes of water (Ministry for the Environment, 2007a).

Levels of bacteria are affected by both natural and human factors. Thus, although the sites measured show improvement, the time series of four years is not long enough to show whether they were the result of human factors or annual weather variations (Ministry for the Environment, 2007a).

 Proportion of swimming sites where 95–100% of samples comply with guidelines, 2003/04 to 2006/07.

Water allocation compared with total water resource (indicator 4.7)

Fresh water is a finite resource, so competing demands for water use must be balanced with maintaining the resource. Water for consumption is allocated by regional councils as maximum volumes over a time period. In 2006, irrigation accounted for 77 percent of allocations, public water supply 11 percent, industrial use 9 percent, and stock watering 3 percent. Irrigation is particularly needed to support agriculture and horticulture in New Zealand.

Between 1999 and 2006, total water allocation in New Zealand increased by 50 percent. Allocation increased for all regions except Northland (see figure 4g). The increase in total allocation was driven by irrigation. The amount of irrigated land increased by 52 percent over the period. In Northland, the decrease in water allocation may reflect changes in the way resource consent information is held rather than an actual reduction (Ministry for the Environment, 2007a).

Water stress at a regional level can be estimated by the ratio between allocation and the total water resource (see figure 4h). This is a proxy measure, and the limitations of the indicator are outlined in the ‘About the indicators’ section below. Commonly used thresholds for water stress (Raskin et al, 1997) are:

  • low – ratio is less than 0.20
  • medium – ratio is between 0.20 and 0.40
  • severe – ratio is higher than 0.40.

Because allocations have increased in all regions except Northland, water stress has also increased. Despite this increase, in 2006 water stress remained low for all regions, except Canterbury, where there was medium water stress (0.22).

 Water allocation by region, 1996 and 2006 December years.

 Water allocation compared with total water resource, by region, 1999 and 2006 December years.

About the indicators

Water data overview

In the context of sustainable development, there are three key water-related areas missing in this topic, due to the lack of available data. One is actual water use, another is time series data for coastal water quality (other than levels of bacteria), and the third is a measure of water’s cultural significance, such as for Māori and traditional food gathering.

Population with drinking water meeting standards (indicator 4.1)

The Drinking Water Standards for New Zealand (Ministry of Health, 2005) outline specific requirements for the protection of drinking water against contaminants, which include three categories:

  • bacterial, for example E.coli
  • protozoal, for example giardia and cryptosporidium
  • chemical, for example arsenic, boron, fluoride, and other chlorinated compounds.

The data is from Environmental Science and Research and is measured for the years ended December until 2005, after which it changed to years ended June. As a result, the period 2006–07 covers the 18 months from January 2006 to June 2007.

People who are not connected to registered water supplies are counted as not complying with standards. Therefore, lack of access to compliant drinking water may be because either the water fails to meet standards, or it is inadequately monitored, or it is sourced from non-registered supplies.

Nitrogen in rivers and streams (indicator 4.2)

Median and percentiles are used to provide a national picture of river water quality. The 5th and 95th percentiles describe the lowest and highest 5 percent of the results. The median is the value for which half of the values are lower and half are higher.

Levels of nitrogen and phosphorus are measured monthly at 77 sites on 35 rivers in the National River Water Quality Network. The network is operated by NIWA. The monitored sites provide information on a specific section of a river (a river reach), rather than the whole river. The network covers a range of sites, which include 45 impact sites (sites downstream of agriculture, forestation, industry, and urbanisation).

Trends for levels of total nitrogen and total phosphorus are reported. Total nitrogen includes nitrate, the dissolved form of nitrogen (measured in indicator 4.5), and total phosphorus includes dissolved phosphorus.

The data is from the Ministry for the Environment.

Biological health of rivers and streams (indicator 4.3)

Data is derived from 66 of the 77 sites that make up the National River Water Quality Network.

Data is available from before 1996 but because of a change in monitoring methods, comparisons of results before and after 1996 require caution. Accordingly, figure 4c only presents data from 1996 onwards.

Lake water quality (indicator 4.4)

Water quality in lakes is measured using the trophic level index, which combines measures of phosphorus and nitrogen levels, visual clarity, and algal biomass. The level of nutrients (trophic level) is summarised as being very low to low, moderate to high, or very high (severely degraded).

Data is from the Ministry for the Environment. Trends in the water quality of lakes have been calculated using the Burns methodology (Burns, Bryers, & Bowman, 2000).

Groundwater quality (indicator 4.5)

Nitrogen is found in groundwater in the form of nitrate and is monitored for health and environmental reasons. The trend data between 1995 and 2006 is from 878 groundwater sites. The median data is based on 956 sampled sites.

The results can be regarded as representing areas where contamination is more likely to occur, rather than representing the overall groundwater resource in New Zealand. This is because the groundwater sites sampled are considered to be both an important source of supply and particularly vulnerable to pollution.

Bacterial pollution at coastal swimming spots, rivers, and lakes (indicator 4.6)

New Zealand’s guidelines for recreational water quality define safe levels of faecal contamination. The bacterial groups monitored are used as indicators of possible sewage contamination.

The period measured is the summer period (November–March) when most swimming occurs. Included in the sample are 380 coastal swimming spots and 230 freshwater sites. These are sites where at least 10 water quality samples have been taken each summer.

Water allocation compared with total water resource (indicator 4.7)

The indicator recommended by the United Nations (2007) to measure sustainable water use is total water abstraction (use) divided by the total volume of water available. However, as good information on water abstraction is not readily available a proxy indicator is used – water allocation divided by the total water resource, by region. Water allocation, differs from water abstraction in that not all water allocated is actually used.

The total water resource for each region is calculated as a mean annual value over the period 1995–2005, from the Statistics NZ water physical stock account. It is calculated as inflow into the region (from precipitation and flows from other regions) minus the loss of water by evaporation, transpiration, and flows to other regions. This is an indirect measure of the total volume of water available as not all the water resources of a region are exploitable. For example, low or base river flows generally need to be left to support ecosystems and other in-stream uses. Also, not all water that is used is lost from the catchment it is taken from.

Table 4.2
Water indicators – defining principles

 Water indicators - defining principles.

See part C for the complete list of defining principles for all indicators.

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