What can a sand filter not remove from water?

A sand filter is designed to physically remove particulate matter from water through a process of filtration. This filtration system is effective for reducing turbidity, which consists of suspended solids that cause cloudiness in the water, as well as floc, which is a clumpy form of particulate matter that results from the coagulation process in water treatment.

However, a sand filter is not capable of removing dissolved substances from the water, including dissolved oxygen. Unlike suspended particles that can be trapped in the filter medium, dissolved oxygen is evenly dispersed throughout the water at the molecular level and cannot be effectively removed by physical filtration methods.

This characteristic of dissolved oxygen—remaining in solution rather than existing as discrete particles—distinguishes it from other contaminants that sand filters target, such as viruses or floc, which are also larger and subject to filtration. Thus, sand filters will not impact the levels of dissolved oxygen in water, making this answer the most suitable choice.