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I have a metal waterline from my dishwasher but a plastic shutoff valve under my counter. Is it OK to connect the metal to plastic?

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  • I am not sure if it affects the answer. Is it cold water or hot water. Commented Aug 7, 2023 at 19:46
  • Both plastics and various metals are used for all manner of plumbing fixtures, pipes, valves, and fittings. They can all be connected together if they are otherwise compatible in size.
    – kreemoweet
    Commented Aug 7, 2023 at 19:59

2 Answers 2

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Yes, it's fine to connect metal to plastic.

The concern that you might be thinking of is connecting dissimilar metals, such as steel and copper, together. This allows galvanic corrosion to occur unless you include a dielectric union.

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Do you know if the supply is cold or hot water? Some dishwashers use hot supply, some use cold.

Generally, plastic valves should only be used for low temperature and low pressure applications. While there probably are plastics that could handle hot water supply, I think it's best practice to only use metal valves. Additionally, the installer should not have mixed the two materials without a proper adapter, as temperature differences and shrinkage/expansion in the two different materials can eventually cause joint loosening or cracks to appear.

Legal requirements will depend on your local plumbing code?

You could also look up the valve to try and identify the specs. For example, this type of valve clearly says "for cold water use only".

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