pipelines. some of these aquifer fed systems such as that serving christchurch was of sufficiently good quality that no disinfection of final water was practised until the recent earthquake events. following restoration of the network the water is no longer chlorinated. water taken from shallower or less secure aquifers are at risk of contamination. water supply volumes and losses the 2018-19 national performance review includes data about water supply volumes from the participants in the study. residential consumption is estimated because only around 50% of residential properties nationwide have a meter installed. water new zealand noted that in this annual review, the total volume of non-residential water use is under-represented, and residential consumption overestimated, as some participants did not provide volumes of non-residential water use. water end usevolume (m3) non-residential water consumption127,184,998 residential consumption estimate316,963,581 total network water loss119,010,271 water supplied to system563,158,850 the median of the average daily water consumption across participants is 263 litres per person per day, but there is a large spread in residential water efficiency in different areas.: 64 in the 2019 fiscal year, participants reported 119 million cubic meters of water was lost in their water supply systems, equivalent to over 47,000 olympic-sized swimming pools. this constituted 18% of the 555 million cubic meters of water supplied to the system.: 57 treatment of drinking water most drinking water supplied through reticulated networks in new zealand is disinfected using chlorination. however, some communities have water sources derived from deep aquifers that they consider are "secure" or low risk without chlorination. there is opposition to chlorination in some of these communities. however, water new zealand, the industry association that represents 1900 water engineers and specialists, advocates for chlorination of all public water supplies. water supplies in new zealand generally have low concentrations of naturally-occurring fluoride, at levels that are insufficient to promote good dental health. fluoridation of public water supplies is undertaken in most public water supplies, typically at a rate between 0.7 and 1.0 mg/l. a report by the office of the prime minister's chief science advisor issued in 2021 confirmed previous studies that showed a positive impact of fluoridation on dental health, and no significant adverse effects. in 2021, the health (fluoridation of drinking water) amendment bill was passed, transferring control over the decision to fluoridate drinking water from local councils to the director-general of health. drinking-water quality havelock north contamination 2016 from 12 to 29 august 2016 the town of havelock north experienced new zealand's largest recorded outbreak of waterborne disease. campylobacter entered the town's water supply. of the town's 13,000 residents, 5,500 fell ill, 45 were hospitalised and four died. inquiry in september 2016, the government announced an inquiry into the outbreak, in two stages. stage 1 focused on identifying what happened, what caused the outbreak, and assessing the conduct of those responsible for providing safe drinking water to havelock north. stage 2 of the inquiry addressed lessons learned for the future and steps to be implemented to reduce the likelihood of such an outbreak occurring again. findings the drinking water for havelock north was sourced from an aquifer under the heretaunga plains (the te mata aquifer) that was thought to be a confined aquifer secure from contaminants. the district council did not treat water drawn from this aquifer before it was distributed to consumers. during a period of heavy rain, a paddock adjacent to the bore became inundated, and sheep faeces caused contamination of the bore water. the inquiry found that in july 1998, there had been a previous incident of contamination of drinking water at havelock north, but that the lessons from that incident had been forgotten. another key finding was that several of the parties with responsibility for the water supply regime for havelock north had failed to adhere to the high levels of care and diligence needed to protect public health and to avoid outbreaks of serious illness. the inquiry concluded that a higher standard of care was needed, similar to that applied in the fields of medicine and aviation where the consequences of a failure could similarly be illness, injury or death.: 8 recommendations the recommendations arising from stage 2 of the inquiry including wide-ranging proposals for legislative and regulatory changes to drive systematic improvements in the management of drinking water nationwide. the recommendations also included mandatory treatment of all drinking water networks and certain self-supplied systems, and the review of drinking water standards and guidelines. subsequent research findings the institute of environmental science and research (esr) carried out genome-sequencing on the campylobacter strain that was found in sick people during the outbreak. the subsequent research has shown that some people living outside havelock north, but who visited the area during the time of the outbreak, were also affected. the study suggests that the total number of campylobacteriosis cases traceable to the water contamination could be as high as 8320, with up to 2230 of these living outside of havelock north. annual drinking-water quality report - 2017-18 the ministry of health provides an annual report on the drinking-water quality of all registered networked drinking-water supplies serving populations of more than 100 people. the report for the period 1 july 2017 to 30 june 2018 describes compliance with the requirements of the drinking-water standards for new zealand and progress made towards meeting the requirements of the health act 1956. performance criteriapopulation water complies with all the legislative requirements under the act3,250,000(84.7%) implementation of a water safety plan for the supply has commenced3,810,000(99.3%) met the bacteriological requirements of standards3,751,000(97.7%) met all the monitoring requirements in the standards3,531,000(92.0%) sanitation all significant sized urban developments are served by municipal sewers which drain to modern treatment works with final discharges to river or the sea. rural communities and isolated housing is served by septic tanks or by chemical toilets or earth closets depending on location and usage. the 135 wastewater treatment plants discharge into the following type of environment: estuary 5 groundwater 8 lake 1 land 26 long sea outfall 22 near shore outfall 7 river/stream/drain 62 wetland 4 stormwater in its summary of the findings from the national performance review 2018–19, water new zealand observed that management of stormwater quality is not yet widespread. stormwater quality monitoring programmes and/or catchment management plans are in place for just over half the review's participants. consents for stormwater discharge are even less widespread. only eight participants had all stormwater discharges consented. most commonly, participants had consents for less than 10% of the network, and six participants had no stormwater discharge consents whatsoever. in 2018, the auditor-general reviewed the management of stormwater by three councils, to gain insights into how these councils were managing the risk of flooding in their communities. the councils reviewed were dunedin city council, porirua city council, and thames-coromandel district council. one of the main conclusions was that the three councils had a reactive approach to understanding flood risk, by relying mostly on the information collected after a flood. the lack of forecasting could lead to a poor understanding of the risk and cost of future events, and inadequate preparation. the review also noted that the three councils were spending less than the annual depreciation amount on re-investment in stormwater systems, and that under-investment could lead to stormwater systems failing to contain and minimise flooding. in the summary of findings, the auditor-general noted that all councils face challenges when managing their stormwater systems, including ageing infrastructure, limited capacity, managing costs to the community, and having the right people and skills in their organisations. the main recommendations concern the need for improved investment decision making, based upon better information about flood risks, and the performance and capacity of stormwater assets.