Baleen-like reverse desalinator made from teeth.
Baleen is a series of keratin screens in the mouth of whales. They take in a mouthful of water + stuff then use pressure to expel the water through the baleen screen. Water moves thru but particles (including very small particles of krill) are retains, which the whale then licks off the inside of the screen.
Reverse osmosis is a method of water purification in which water is pressurized against a filter that has pores small enough to admit passage of water molecules but nothing larger. Completely pure water emerges through the filter with wastes being concentrated in the water remaining on the pressurized side, and later discarded. Reverse osmosis filters need to be able to withstand pressure. They are often ceramic and look like porcelain.
Your GMO people contain water in their mouth - maybe anterior to the teeth, and generate powerful suction, pulling the water against the teeth. The teeth are modified to be porous in the way of a RO filter. The water they pull thru is pure. Water remaining anterior to the teeth has concentrated pollutants, and is expectorated.
Drinking like this takes some time because it must be sip by sip. You people entertain themselves by competing to see who can spit the toxin-laden water farther. Some of them are genetically engineered to have far spitting abilities as well.