The water purifier lets you drink your own urine. Sold as part of the Ammunation Apocalypse Kit in Grand Theft Auto 5

The Water Purifier is a product in Grand Theft Auto V

It is part of the Ammunation Apocalypse Kit

This purifier lets you purify your own urine, making it drinkable and allowing you to survive longer when there is a shortage of water, such as in an event of a Zombie Apocalypse.