Where do you get that from? According to https://zerowater.com/pages/frequently-asked-questions,

> Does the ZeroWater® 5-stage filter reduce bacteria?

> The current system is meant to be used with municipally treated, potable water as the current filter will not remove microbiological contaminants.

> Does the ZeroWater® 5-stage filter reduce cryptosporidium?

> At this point ZeroWater® 5-stage filters have not been tested for the removal of cryptosporidium(microbiological cysts).

Both ZeroWater and Brita are explicit that their filters are meant to be used with water that the government has already deemed safe to drink.

I didn't check my sources correctly. I googled and blindly repeated a non reputable site. Mea culpa

How do you "filter" heavy metals? They would, I think, be in solution, so it should not be possible to remove them with a filter. (I know the ZeroWater company claims that, but I'd have to know what the basis is for that claim.)

ZeroWater uses a mixed bed ion exchange resin (anion and cation) to attract and hold dissolved ionized solids. Mixed bed resin is very effective and will remove nearly 100% of dissolved solid content which will includes all heavy metals.

The downside of mixed bed resins is that they are not selective and water with high dissolved content (TDS) will deplete the resin at very fast rate. Price per gallon is comparable to bottled water with moderate to high TDS. They are simple and very effective as long as the filter is replaced as needed.

Ion exchange resin, I imagine.