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• Drinking water quality

Drinking water quality

Relevance

Maintaining good drinking water quality is critical for human health and quality of life outcomes. The health risk to consumers from water-borne diseases in drinking water supplies comes from three main types of microorganisms: bacteria (such as Campylobacter and pathogenic E. coli), parasites (such as Giardia and Cryptosporidium) and viruses such as the Norovirus. Improvements in this indicator suggest less of the population is at risk of water-borne diseases and other microbiological contaminants.

Current level and trends

Most New Zealanders are supplied with drinking water that complies with the microbiological standards. However, many smaller communities are supplied with microbiologically non-compliant drinking water. In 2005, the proportion of the total population whose drinking water, measured at the tap, complied with the 2000 Drinking Water Standards for E. coli was 76 percent. This was an increase from 74 percent in 2004 and a considerable improvement from 63 percent in 2001. Most water supplies serving large population areas are fully compliant with the 2000 standards. A significant reason for non-compliance is inadequate monitoring rather than proven contamination of drinking water.

Compliance with the 2000 Drinking Water Standards for Cryptosporidium is assessed at the water treatment plant rather than at the tap. In 2005, the Cryptosporidium compliance rate was 61 percent.⁸⁰ This was slightly up on the 2004 rate of 60 percent and an improvement on the 2001 rate of 52 percent. Compliance rates fluctuated between 48 percent and 61 percent over the 2001–2005 period. The drop in the compliance rate from 2002 to 2003 was largely due to non-compliance at the Waitakere plant, which has since been resolved. 

Figure EN2.1 Proportion of the total population served with water that meets the 2000 Drinking Water Standards, 2001–2005

Source: Water Information New Zealand Database, March 2007

Regional differences

Groundwater sources supply drinking water for approximately 40 percent of the New Zealand population; about 60 percent of people are supplied from surface water. Most water in catchment headwaters is of good quality. Lower down the catchment, where farming and intensive land use occurs (eg intensive livestock farming), water quality deteriorates. Problems with the quality of some groundwater sources have also been identified.

There is considerable regional variation in the population served with drinking water that is fully compliant with the 2000 Drinking Water Standards for E. coli and Cryptosporidium. In 2005, only 5 percent of the population in the Marlborough region was served with drinking water that fully complied with the 2000 Drinking Water Standards for E. coli. The Northland and the West Coast regions also had low compliance rates, with 28 percent and 35 percent of the population respectively supplied with drinking water that was fully compliant. Compliance was highest in the Nelson region (92 percent), followed by the Auckland region (91 percent) and the Wellington region (85 percent). 

In 2004, none of the population in the Marlborough region was supplied with drinking water that fully met the 2000 Drinking Water Standards for Cryptosporidium. Less than 1 percent of the population both in the West Coast and Gisborne regions were supplied with fully-compliant water. Compliance was highest in the Nelson region (92 percent), followed by the Auckland region (88 percent) and the Hawke’s Bay region (82 percent).

International comparison

Overall, the quality of New Zealand's water is comparable with other developed countries. New Zealand's water supplies are free of many of the pathogens that result in sickness and death in other countries. However, the incidence of Giardia infection in New Zealand is 85 per 100,000 people, which is considered high compared to the reported rates for other western countries.⁸² The contribution of contaminated drinking water to the incidence of giardiasis is not known.