Taste & Odor (Secondary Standard, Odor: <3 TON [Threshold Odor No.])
Most taste is actually odor, and it was found that a Threshold Odor Number of 3 (a 3:1 dilution 1 with odor-free water makes the bad T&O disappear) is the maximum most people would tolerate before abandoning a water supply (perhaps in favor of a Jess safe supply). The predominant bad T&O in potable water these days is that of chlorine in some form. Second is the very common “musty-earthy-moldy-meldewy-fishy” T&O produced by certain algae, bacteria, and molds. Other fairly common offenders are iron and sulfur compounds already discussed above, other strange T&O occasionally produced by microorganisms, and the strong medicinal T&O of chlorophenols that sometimes plagues systems using marginal disinfection practices. Each of these will be discussed below.