What is the effect of proper coagulation on the clarity of water?

The correct choice highlights how proper coagulation significantly enhances the clarity of water. Coagulation is a process where chemical coagulants—such as aluminum sulfate or ferric chloride—are added to water to neutralize the charges of suspended particles, thereby allowing them to clump together, or "coagulate."

Once these particles join and form larger aggregates, they can more easily settle out of the water or be filtered out, significantly reducing turbidity. This removal of small particles, which are often responsible for murkiness, leads to clearer water. Proper coagulation not only boosts the aesthetic quality of water but also improves its safety by facilitating the removal of pathogens and other contaminants that can be associated with turbidity.

The other possibilities do not accurately represent the effects of coagulation. Decreasing clarity or no effect on clarity contradicts the fundamental purpose of coagulation in water treatment, while the notion that it makes the water appear darker does not align with the actual outcomes of the coagulation process. Overall, effective coagulation is vital to achieving cleaner, clearer water, thereby supporting public health and environmental quality.