Removing iron and manganese from drinking water instead of sequestration it is recommended if the water contains over 0.3 ppm of iron or 0.05 ppm of manganese. These elements can be removed during softening with lime, but most commonly iron and manganese are removed by filtration after oxidation (with air, potassium permanganate, or chlorine). Gravity and pressure filters are both used, with pressure filters being more popular.
The operator should frequently check to see that all the iron in the water entering the filter has been converted to the ferric (or insoluble particulate) state. The operator collects a water sample, passes it through a filter paper, and runs an iron test on the clean, filtered water (filtrate). If no iron is present, it has all been oxidized and is being removed in the filtration process. If iron is found in the filtrate, oxidation has not been completed and some of the iron will pass through the filter and end up in the treated water. In this case, the operator should consider adjustments to the oxidation process.
Most iron removal filters are designed so that the filters are backwashed based on head-loss on the filter. If an iron breakthrough is a problem, the filters will have to be backwashed more frequently. Accurate records will reveal when a breakthrough is expected so that the operator can backwash before it is likely to occur.