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  • Rights: The University of Waikato Te Whare Wānanga o Waikato and Waikato Regional Council
    Published 17 March 2020 Referencing Hub media

    In chemistry, pH is a number that expresses the acidity or alkalinity of a solution. A neutral solution has a pH of 7. Acidic solutions are those with a pH less than 7, and basic solutions are those with a pH greater than 7.

    pH affects drinking water supplies. Water with low pH can corrode or dissolve metals such as pipes. Water with high pH may taste bitter, leave mineral deposits in pipes and appliances and require additional chlorine to disinfect for drinking water.

    In aquatic ecosystems, changes in pH levels can stress organisms and reduce hatching and survival rates. Changes in pH can also increase the solubility of nutrients like phosphorus and make them more accessible for plant growth, which may lead to algal blooms.

    Contaminants from spills and from land use can affect the pH of water.

    Dr Eloise Ryan discusses pH as an indicator of water quality.



    Water has a neutral pH of pH7. So in streams, if pH is too high, that means it can affect aquatic life. So if we add in a chemical contaminant such as ammonia, that can increase the pH and affect fish life, or if a contaminant like an acid gets into the water, that can decrease the pH and make it acidic and affect the ecosystem as well. If there’s large algae blooms, that can affect the pH as well, because algae are plants, and they photosynthesise. So during the day that drives the pH down, and then at night when they respire, it drives the pH the other way. So you can have huge pH fluctuations in water bodies, and that can affect fish quite negatively. So it’s very important for waterways to try and remain in neutral pH.


    Dr Eloise Ryan
    Waikato Regional Council
    Footage of algae mats in river, Cawthron Institute


    This video has been developed in partnership with the Waikato Regional Council as part of the Rivers and Us resource.

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