WA premier Mark McGowan says he will not allow Alcoa’s bauxite mining to threaten drinking water supplies, casting doubt on the long-term future of the US aluminium giant’s operations in the state.

Mr McGowan was forced to take a public stand after it was revealed, by WAtoday, that for the past two years experts within his government have warned that a major dam and source of Perth drinking water is at an unacceptable risk of contamination.