A Water Bob is a food grade plastic bag that you can put in your tub to collect drinkable water. This is useful if you believe you will have a power outage or if you believe your pipes will freeze and you will not have access to drinkable water. We just experienced a severe polar vortex, and our pipes did freeze, and we are going to have a few more very frigid nights. To make sure we had potable water we did purchase water flats, and we put our Water Bob in the tub. The Wa