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  • The factors that affect water quality include where the water comes from, what is in the environment in the collection area and how it is treated.

    Rights: © Plamen Petrov, licensed through 123RF Limited.

    Drinking water

    In New Zealand, we take for granted our access to high-quality drinking water, but a lot of research and effort goes into making sure that the water we drink is not going to makes us ill.


    New Zealand gets its drinking water from many different sources, depending on what area you live in. You could get your drinking water from surface water (rivers, streams, lakes, reservoirs), groundwater from aquifers (bores/wells, springs) or rain water. New Zealanders also like to play in and around water such as rivers, beaches and lakes – this is called recreational water.


    Each lake, river, stream and reservoir receives water that drains into it from the surrounding land. This surrounding land is called the catchment area for that water body. Smaller streams and rivers contribute their water to larger lakes and rivers, which may mean that the total catchment area of your local lake or river is much further away and larger than you may think.

    Rights: Public domain – worldwideTobias Thierer

    Lake Hawea

    Lakes fill with water from rain or snow falling on the surrounding land. This surrounding land is called the catchment area, and the nature of the land in this area contributes to the quality of the water in the lake.

    The environment around the catchment area for water has an impact on its quality. If the catchment area includes farms, especially cattle grazing to the water’s edge, the water quality will be affected by sediment being stirred up and by animal faeces contaminating the water. The use of chemicals such as pesticides and fertilisers on surrounding farmland may also introduce contaminants into surface waters and groundwater. If the catchment area includes built-up areas with a lot of people, including all sites upstream, then sewage may get into the water from leaky pipes, septic tanks and storm overflows. The household use of chemicals, such as detergents, cleaners and petroleum based chemicals, may also introduce contaminants in water sources.

    The effect of sediment on water quality

    Dr Chris Nokes discusses the effect sediment can have on microorganisms in the water. It is possible that microorganisms survive longer in sediment than they do in water, and when it rains, this sediment is stirred up and the water becomes difficult to treat.

    Nature of science

    Multiple factors often need to be considered when treating substances to make them suitable for human use. Often there are several treatment processes that target different properties of materials that allow them to be processed, for example, many substances can dissolve in water or float or not be wanted in the water. Water is also a good medium for microorganisms to grow in.

    Another factor affecting the water quality is industry – factories have strict guidelines for disposal of waste and can be heavily fined if caught not obeying these guidelines, but accidental spillages are still a possibility. The chemistry of the soil and rocks in water sources can also affect the water quality. Some areas, for example, are naturally high in ‘heavy metals’ such as arseniciron and manganese.

    How can water spread disease?

    Dr Chris Nokes describes why it is important that we manage our water resource so that disease-causing organisms are eliminated from our drinking and recreational water.


    The treatment of the water you receive depends on where it is gathered and what has affected it on its route. For example, in Christchurch, the drinking water is groundwater that has effectively been filtered naturally through alluvial gravel for 10 to 700 years and is not treated at all.

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    Water pollution

    Industrial use of chemicals can contaminate waterways. There are strict guidelines in place to ensure that chemicals are used and disposed of in a manner that will not affect the environment.

    Water supplies ideally use multiple barriers to ensure you get safe drinking water.

    • The first barrier is protection of the water in the catchment. This may consist of fences to keep stock from the water source. Farmers may be restricted in their use of aerial crop spray. People may also be kept from using the body of water for recreational purposes.
    • The second barrier is carried out in the treatment plant and consists of processes to remove particles from the water. The coagulationflocculation treatment step causes sediment and other fine particles to group together to form clumps. These clumps can then be settled or filtered out.
    • The third barrier is a disinfection step. This is done to kill any pathogens that may be in the water. It can be done by adding chemicals such as chlorine or ozone, or by exposing the water to ultraviolet (UV) light. It is very important to remove particles before the disinfection, otherwise the disinfection may not work very well.
    • The last barrier is a post-treatment step and is the maintenance of pipes and tanks so that nothing can recontaminate the water.

    Water quality is regularly monitored throughout New Zealand by local, regional and national agencies.

    What is flocculation?

    Dr Chris Nokes describes how adding a flocculant coagulant to muddy water causes the mud particles to group together to form larger heavier clumps that can then be filtered or settled out of the water. This flocculation-coagulation step makes it easier to treat the water to kill any microorganisms that may be present.

    Related content

    Read the article Water quality – factors and issues to find out about who monitors our water quality and what they measure. The interactive Water quality indicators features several of the physical and biological indicators that scientists use to assess water quality.

    Find out how some of our daily interactions can impact our local waterways with the interactive Our use of water – impacts on water quality, then find out some of the issues that roads, businesses and primary production can have on water quality.

    Learn more about catchments with the interactive Water flows and catchments. It curates catchment information and activities in one location.

    Find out about the steps taken to protect water supplies from aerial 1080 operations and the fate of 1080 in streams in the article 1080 and water quality.

    Activity idea

    Find out how some of the Waikato residents get clean drinking water with the activity Getting water ready to drink.

    Useful links

    The following sites provide information and worksheets for investigating the health of your local stream, search for ones in your area if it is not below:


    In 2018, the Christchurch City Council began temporarily treating Christchurch's water with chlorine while it upgrades the below-ground well heads. This provides an extra level of protection against waterborne illnesses.

      Published 8 January 2009 Referencing Hub articles
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