Direct filtration can be used effectively when the source water is low in which of the following?

Direct filtration is most effective when the source water is low in turbidity, color, algae, and coliforms because this process relies on the physical removal of particles and microorganisms through the filter medium. When these contaminants are present in high concentrations, they can overwhelm the filtration system, leading to potential inefficiencies and possible breakthrough of contaminants into the treated water.

In the context of direct filtration, turbidity is particularly critical since it can indicate the presence of suspended particles that could clog filters and reduce their effectiveness. A reduction in color and algae also enhances the quality of the water being treated, as these can contribute to additional burdens on the filtration system. Coliform bacteria serve as an indicator of potential pathogenic contamination; thus, lower levels allow for greater confidence in the filtration process.

In essence, when source water contains minimal levels of these specific contaminants, the direct filtration process can operate efficiently, ensuring the treated water meets safety standards and is suitable for consumption.