Media release

17 November 2004

Tightening of Ministry of Health Cryptosporidium drinking-water standards delayed

A new Ministry of Health water standard that would lower the existing limit of the fine particles in drinking water left over from filtering and treating it, has been deferred.

The new standard, which was planned to be in force by the first of January next year, sets lower limits for turbidity (due to particles) to reduce the risk from Cryptosporidium, a common contaminant in New Zealand waters. This can cause diarrhoea and other more serious problems in some people.

A set of revised water standards will come into force in July 2005. They will allow alternative ways of reducing the risk from Cryptosporidium from water treatment plants that cannot meet the new turbidity standard.

To enable suppliers to take advantage of the new options in the revised standard, the planned amendments will be delayed until July 2005.

Background

The Drinking-Water Standards for New Zealand 2000 required that by 1 January 2005, 95 per cent of turbidity measurements on the filter effluent from a chemical coagulation and filtration treatment unit should not exceed 0.1 turbidity units (NTU).

This target was set to protect drinking-water consumers from Cryptosporidium. This standard was based on chemical coagulation and filtration being the only treatment received by the water.

New knowledge has made it possible to incorporate an allowance for the additional effect of other types of treatment in the revised Drinking-Water Standards for New Zealand 2005. This will provide alternative options for providing protection from Cryptosporidium. With these additional treatments in place, sufficient protection against Cryptosporidium is provided and it is not be necessary for the 0.1 NTU turbidity requirement to be met.

Accordingly, the Director-General of Health has authorised the 0.1 NTU requirement that was due to come into effect on the 1 January 2005 being held in abeyance until the revised Drinking-Water Standards for New Zealand 2005 come into effect on 1 July 2005.



Deferment of 0.1 NTU Turbidity Target in Drinking-Water Standards for New Zealand 2000

The Drinking-Water Standards for New Zealand 2000 required that by 1 January 2005, 95 per cent of turbidity measurements on the filter effluent from a chemical coagulation and filtration treatment. unit should not exceed 0.1 turbidity units (NTU).

This target was set to protect drinking-water consumers from Cryptosporidium. This standard was based on chemical coagulation and filtration being the only treatment received by the water.

By incorporating an allowance for the additional effect of other types of treatment in the revised Drinking-Water Standards for New Zealand 2005, it will not be necessary for the 0.1 NTU turbidity requirement to be met.

Accordingly, the Director-General of Health has authorised the 0.1 NTU requirement that was due to come into effect on the 1 January 2005 being held in abeyance until the revised Drinking-Water Standards for New Zealand 2005 come into effect on 1 July 2005.

Background

The Drinking-Water Standards for New Zealand 2000 that were released by the Director-General of Health in 2000 prescribed the following protozoa compliance criteria for chemical coagulation and filtration treatment:

<“Protozoa criteria (b) applicable for chemical coagulation and filtration treatment

• Measurements of the turbidity of the water leaving each filter satisfies the following requirements:
  

(i) 95 percent of the turbidity measurements over the reporting period (at the frequency specified in Table 3.4) do not exceed 0.5 NTU1, and

(ii) at any time during a filter run (excluding any period of filtering to waste) the turbidity does not exceed 1.0 NTU 2 and for continuous monitoring³, no increases of more than 0.2 NTU shall occur in any 10 minute period, except that up to two turbidity records per day may exceed 1.0 NTU⁴ to allow for spurious peaks.

These criteria were to be amended at 1 January 2005 as follows:

1 As at 1 January 2005 this value will become 0.1 NTU

2 As at 1 January 2005 this value will become 0.5 NTU

3 As at 1 January 2005 all drinking-water suppliers servicing more than 10,000 people will be required to continuously monitor their filters and all filters must give an alarm to duty staff in the event of transgression].

4 As at 1 January 2005 this value will become 0.5 NTU.”>

In the revised Drinking-Water Standards for New Zealand 2005 it is proposed to adopt a cumulative credit system for assessing compliance with the protozoa standards. This will provide alternative options for the demonstration of compliance with the protozoa criteria. A slightly lower performance of a chemical coagulation and filtration treatment process than that required by Protozoa criteria (b) will be acceptable provided that this treatment is augmented by others that, in total, accomplish the same degree of protozoa removal as the Drinking-Water Standards for New Zealand 2000 Protozoa criteria (b) provides.

The Expert Committee on drinking-water quality standards has therefore recommended to the Ministry that, as an interim provision, the deadline for the above amendment be postponed until the Drinking-Water Standards for New Zealand 2005 become operational, when the 2000 standards would be superseded.