Drinking water quality

Relevance

Good quality drinking water is critical for people’s health and their quality of life. 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 Norovirus. Improvements in this indicator suggest less of the population is at risk of water-borne diseases and other microbiological contaminants. In 2006/2007 there were 27 water-borne disease outbreaks, with untreated or contaminated supplies identified as a contributing factor in most of them.⁹⁶

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 2007/2008, the proportion of the total population whose drinking water, measured at the tap, complied with the Drinking-water Standards for E. coli was 83 per cent. This was an increase from 79 per cent in 2006/2007 and a considerable improvement from 63 per cent in 2001. Most water supplies serving large population areas are fully compliant with the Drinking-water Standards. A common reason for non-compliance is inadequate monitoring rather than proven contamination of drinking water.

Compliance with the Drinking-water Standards for Cryptosporidium is assessed at the water treatment plant rather than at the tap. In 2007/2008, the Cryptosporidium compliance rate was 66 per cent. This was similar to the 2006/2007 rate of 67 per cent, but an improvement on the 2001 rate of 52 per cent. Compliance rates for Cryptosporidium dropped in 2003 to 47 per cent, but recovered to 59 per cent in 2004. The drop in the compliance rate in 2003 was largely due to non-compliance at the Waitakere plant, which has since been resolved.

Figure EN2.1 Proportion of the population served with water that meets the relevant Drinking-water Standards, 2001–2007/2008

Source: Environmental Science and Research, customised data
Notes: (1) The measurement of compliance moved from a calendar year to a fiscal year in 2006 (2) These compliance rates may differ from those published by the Ministry of Health due to methodological differences explained in Appendix 2

Regional differences

The current transition between the 2000 and 2005 Drinking-water Standards is scheduled to take several years to complete, with drinking water suppliers choosing which of these standards to operate under in the meantime. Therefore, some regions will have moved to the 2005 standards while others will still be using the 2000 standards.

There is considerable regional variation in the population served with drinking water that is fully compliant with the 2000 or 2005 Drinking-water Standards for E. coli and Cryptosporidium. Between 2002 and 2005, less than 5 per cent of the population in the Marlborough region was served with drinking water that fully complied with the Drinking-water Standards for E. coli. In 2006/2007 this increased significantly to 75 per cent and remained at that level in 2007/2008. The West Coast and Tasman regions have had compliance rates with E. coli standards below 50 per cent since 2004. Compliance was highest in the Nelson (97 per cent), Canterbury (91 per cent) and Auckland (90 per cent) regions.

In 2007/2008, none of the population in the Marlborough and Gisborne regions was supplied with drinking water that fully complied with the Drinking-water Standards for Cryptosporidium. None of the population in Marlborough has had drinking water that complied with the standards for Cryptosporidium since the data series started in 2001. In 2007/2008, 1 per cent of the population in the West Coast region and 4 per cent of the population in the Tasman region were supplied with fully-compliant drinking water. Compliance with Cryptosporidium standards was highest in the Nelson (96 per cent), Auckland (87 per cent) and Wellington (83 per cent) regions.

International comparison

Overall, the quality of New Zealand’s drinking 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 some parts of the world. However, the annual average incidence of notified cases of Giardia infection in New Zealand between 1997 and 2006 was 44.1 cases per 100,000 people, considerably higher than reported rates for other western countries, such as the United Kingdom, with 5.5 cases per 100,000 in 2005.⁹⁷ The incidence of notified cryptosporidiosis between 1997 and 2006 was also higher in New Zealand (22.0 cases per 100,000) than in some other western countries, such as Australia (15.8 cases per 100,000 in 2005) and the United Kingdom (8.5 cases per 100,000 in 2005).⁹⁸ The contribution of contaminated drinking water to the incidence of giardiasis and cryptosporidiosis is not accurately known.

» View technical details about the drinking water quality indicator