Corrosion Of Galvanized Potable Water Piping

I.D. of a galvanized carbon steel nipple from the cold water inlet connection of a residential water heater. Tubercles have formed on the I.D. in low flow conditions. Underneath the tubercles are deep corrosion pits. The cold water chemistry exhibited a Langelier Index of - 0.31 and contained 8 ppm of dissolved oxygen