You may remember from an earlier EarthDate that seawater is so salty, drinking it pulls water from the rest of your body, which can lead to dehydration and even death.

To keep their ships stocked with fresh water, sailors have relied on innovation and technology for centuries.

Early on, they realized they could funnel rainwater from their sails into storage—once the rain had washed away the ocean spray.

Greek sailors then discovered they could hang sheep pelts in the cool night air to absorb water vapor, then wring them out in the morning for a wool-flavored drink.

The earliest European sailors used barrels laced with alcohol to keep algae from growing.

Whenever a ship reached land, replenishing its fresh water was usually the most important task.

By the 1700s, inventors had created distillation plants that used a heat source to boil seawater. When it converted to steam, it left the salt behind. The vapor would then condense again into pure distilled water.

Distillers were used until 1980, when they were replaced by reverse-osmosis systems that use membranes to purify and desalinate water.

Today, navy fleets of about 50 ships have the capacity to desalinate more than a million gallons of water a day.

Cities with large naval bases, like San Diego, are looking at ways to use their fleets’ desalination capacity to supplement their municipal water systems in times of drought and other emergencies.