The primary use of a sand filter is to:

A sand filter serves multiple important functions in the treatment of water, primarily focusing on the physical and biological removal of contaminants. The answer encompasses both the removal of suspended solids and bacteria, which are crucial processes in maintaining water quality.

The filtration process involves the passing of water through a bed of sand, which physically traps larger particles and suspended solids. This step reduces turbidity and improves the clarity of the water, making it visually cleaner and more appealing.

In addition, the sand filter supports biological activity; microorganisms naturally present in the filter media can effectively decompose organic matter and remove bacteria from the water as it flows through. This biological activity enhances the overall treatment efficacy, contributing to the removal of pathogens and promoting a healthier water source.

While it is important to note that sand filters do not completely sterilize water, as sterilization implies a complete destruction of all microorganisms, they significantly reduce the populations of harmful bacteria, thereby improving the safety of the water for various uses. Hence, the comprehensive capabilities of sand filters justify the selection of the option that includes both suspended solids and bacteria removal.