Global mining company Alcoa has been given a stern warning after concerns it was putting one-fifth of Perth's drinking water at contamination risk.

State Government documents have highlighted the increased hazard posed by the resource giant's Bauxite operations near Serpentine Dam. 

Vice President of Transformation Rob Bear told Gary Adshead there are a number of issues that have risen as part of the process of going back and forth, but they're being worked through.

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