What form of ion typically passes through a sand filter and causes dirty water complaints from customers?

The issue of dirty water complaints from customers can often be attributed to specific contaminants that are not effectively removed by filtration systems. Among the options listed, ferrous bicarbonate is particularly relevant because it consists of dissolved iron, which can impart a reddish or brownish color to the water when present in significant concentrations.

When ferrous bicarbonate is oxidized in the presence of oxygen, it can convert to ferric hydroxide, which is not soluble in water and precipitates out, leading to visible particles that are seen as cloudy or dirty water. This phenomenon typically occurs in groundwater supplies where iron is commonly found, especially in sandy aquifers that may allow these dissolved ions to pass through filtration systems without adequate treatment.

Filtration systems, like sand filters, may not effectively capture these ions when they are in their dissolved state, leading to customer complaints about the appearance of the water. Addressing the concerns around ferrous bicarbonate often involves implementing additional treatment processes such as oxidation and filtration to remove the precipitate before it reaches the distribution system, thereby improving the water quality and customer satisfaction.