Rapid pressure changes in a distribution system can cause red water due to precipitation of which iron species?

Rapid pressure changes in a distribution system can cause red water due to precipitation of which iron species?

• A. Fe(OH)2
• B. Fe2O3
• C. FeOH
• D. Fe(OH)3

Answer: (D)

Red water happens when dissolved iron in water is oxidized and then precipitates as a ferric hydroxide. In distribution systems, rapid changes in pressure and the resulting turbulence bring in oxygen and promote the conversion of soluble Fe2+ to Fe3+. At typical drinking-water pH, Fe3+ quickly hydrolyzes to Fe(OH)3, which forms as a gelatinous, reddish-brown precipitate that remains suspended and discolor water. Fe(OH)2 would be greenish and form under reducing conditions, Fe2O3 is a solid rust form but is not the primary suspended compound causing the red tint, and FeOH is not a common stable species in water. So the red water is due to Fe(OH)3 precipitate.

Red water happens when dissolved iron in water is oxidized and then precipitates as a ferric hydroxide. In distribution systems, rapid changes in pressure and the resulting turbulence bring in oxygen and promote the conversion of soluble Fe2+ to Fe3+. At typical drinking-water pH, Fe3+ quickly hydrolyzes to Fe(OH)3, which forms as a gelatinous, reddish-brown precipitate that remains suspended and discolor water. Fe(OH)2 would be greenish and form under reducing conditions, Fe2O3 is a solid rust form but is not the primary suspended compound causing the red tint, and FeOH is not a common stable species in water. So the red water is due to Fe(OH)3 precipitate.