What term describes the ratio of weight of a substance to the weight of an equal volume of water?

The correct term that describes the ratio of the weight of a substance to the weight of an equal volume of water is specific gravity. Specific gravity is a dimensionless quantity that indicates how heavy a substance is compared to water. When calculating specific gravity, the weight of the substance is measured and then compared to the weight of an equivalent volume of water, which is crucial in various fields, including sewage treatment, to assess the buoyancy and behavior of different materials in water.

This measurement is particularly important in sewage treatment as it helps in determining how solids will behave in the treatment process, aiding in the design of equipment and processes for effective waste management. Understanding specific gravity also helps in identifying the concentration of solids and the efficiency of separation processes in treatment facilities.

Density is related, as it also measures the mass per unit volume of a substance, but it does not specifically compare it to water. Volume ratio and weight ratio do not accurately define the concept in question and therefore are not applicable.