Toxic substance is any liquid, solid or gas, which when introduced into the water supply creates, or may create a danger to health and well being of the consumer. An example is treated boiler water. A non-toxic substance is any substance that may create a non-health hazard and is a nuisance or is aesthetically objectionable. For example, foodstuff, such as sugar, soda pop, etc. Therefore, you must select the proper device according to the type of connection and degree of hazard. There are five basic products that can be used to correct cross connection.