On a tour of the plant, John points to the riverbank, where water from the Delaware comes in looking murky — what the experts call highly turbid. Turbidity is just one measure of water quality. Federal rules say drinking water has to be less than 1 nephelometric turbidity unit, known as NTU. The Schuylkill water often clocks in at 30 NTUs because it is fast flowing and picks up more sediments than the Delaware, which often runs about 10 NTUs. The Baxter plant usually reduces it to below 0.3, which is pretty clear.