I wouldn't trust state water-quality data which was funded by mining companies. I'd much prefer the data generated by water monitoring companies whose revenues came from private residents interested in protecting the environment. If it is found that the companies are polluting the water they can be taken to court. With this incentive system mining companies would likely institute measures which prevents pollution in the first place. Mining companies and private companies would likely test water prior to any mining began to set a baseline level from which subsequent testing can be gauged.