Fracking companies may use the chemical additives to thicken or thin the fluids, improve the flow of the fluid, or kill bacteria that can reduce fracturing performance. A large amount of the knowledge comes from studies of water chemistry. Water chemistry is important because several factors about water to be treated and then distributed or returned to the environment are determined through simple chemical analysis. The resultant accumulation by settling is referred to as sediment or biosolids or residual solids in wastewater treatment vessels. The water molecule that gains the hydrogen ion becomes a positively charged hydronium ion. Water dissolves polar substances better than nonpolar substances. Natural water can contain a number of substances or constituents in water treatment operations. When a particular constituent can affect the good health of the water user or the environment, it is considered a contaminant or pollutant.