Wet scrubbing was the original type of scrubbing system. In a common wet scrubber system, the gas is funneled through an area where a wet substance is actively sprayed. Water is used when the gas needs dust and particulate matter removed. Sometimes, other chemicals are added that specifically react with certain airborne contaminants. Since this process adds so much vapor to the exhaust, if the gas is vented, it typically looks like billowing white smoke.