FYI: charcoal filters can introduce arsenic and also appear to increase the bacteria in the filtered water.
"since Oct. 15, 2009, no company is allowed to manufacture, distribute, ship or sell any products that leach arsenic in concentrations greater than 5 parts per billion (ppb)" [1]
And bacteria growth is solved by following the manufacturer's directions. For example, Brita filters in use need to be kept in the fridge and changed every 2 or 3 months.
[1] https://www.wqpmag.com/water-testing/testing-services/articl...
A majority of the water filters purchased on Amazon are not NSF certified and ship with a prop 65 warning. In fact, it's difficult to purchase water filter components that do not have a prop 65 warning.