The solution to keeping our eyes moist is having eyelids and using them to blink. This makes sense — fish and most aquatic animals don’t have eyelids and don’t blink — their eyes are always moist.

Our eyes produce about 10 ounces of fluid per day (nearly the amount in a canned beverage) or about 30 gallons per year. All those tears drain into our tear ducts at the bottom of our eyes and are carried to our nasal passage where they evaporate or get absorbed or drain down to our throats where they’re swallowed. For more, read Why We Have Eyelids, Produce Tears, and Blink.