Inhibition of Copper Pitting Corrosion in Aggressive Potable Waters

Table 1

Typical ranges of constituents in source and treated waters, and ranges in which copper may be susceptible to pitting in chlorinated, high pH, and low alkalinity water. Bolded values correspond to observations in the current work.

Constituent	Presence in potable water	Typical source water range (mg/L)	Typical treated water range (mg/L)	Pitting susceptibility (mg/L)
Free chlorine (as Cl2)	Added as disinfectant	0	1–4, [20]	≥ 0.4; ≥1^A, [21]; ≥2, [22]
Alkalinity (as CaCO3)	Natural constituent; sometimes added or removed via various treatment processes	0-400^C, [23]	Generally similar to source water	≤105^B, [3]; ≤150
Phosphate (as P)	Natural constituent or introduced by pollution; often added as general corrosion inhibitor for various distribution materials	0-0.5^C, [23]	≤1, [24]	≤ 0.1
Silica (as Si)	Natural constituent; sometimes added as corrosion inhibitor; sometimes removed due to treatment interferences	5-55^C, [23]	Generally similar to source water	≤ 5
Organic matter (as TOC)	Natural constituent or introduced by pollution; removed due to taste/odor; disinfectant by-product and/or microbial issues	0-10^C, [23]	1-10^D, [25]	Undetermined; dependent on type of organic present

^ADetermined in short-term, stagnant CMEA tests at pH 9, 34 mg/L alkalinity (as CaCO₃) [21].
^BDetermined in long-term, continuous flow pipe-loop tests at ∼pH 9, ∼0.5 mg/L Cl₂, 25 mg/L DIC [3].
^CIdentified as range between 5th and 95th percentiles from USGS National Water Quality data (groundwater, spring, stream) collected between 1991 and 2011 [23]; alkalinity and Si are not regulated and thus typically occur at similar concentrations in source and treated potable waters.
^DIdentified as range between 5th and 95th percentiles from 1987 AWWARF utility survey [25].