Liberals. Conservatives? That's a different EPA standard.
As far as arsenic, a semi-metal, is concerned, caution is in order, as it can do some weird and often bad things to us.
One of the more recent discoveries is that it can dull our immune response to novel pathogens, giving them more opportunity to establish themselves. And then, when the immune system finally does react, it tends to overreact, which can be just as harmful to us as the pathogen.
Some bright boy came up with a fairly simple system by which people in rural India, whose groundwater is heavily contaminated with arsenic, can clean it before drinking.
It just takes two buckets, a smaller one and a larger one, with some holes in them. In the smaller one is a cheap iron powder, because iron binds with arsenic to form large molecules. The outer bucket has clean sand in it, that traps these large molecules. The water that comes out has lost almost all its arsenic.