We live in a thirsty world. According to the World Health Organization, each person on earth needs 50 liters of water each day for drinking, washing, food preparation and sanitation. And freshwater supplies are dwindling. The National Aeronautics and Space Administration (NASA) reports 21 of the world’s 37 largest aquifers are being depleted faster than they are being replenished.
The water table is dropping, and reversing the trend, we are told, would take hundreds of years. Some steps have already been taken. Bermuda has been collecting rainfall from roof runoff for years, and Brazil has used tropical collection ponds to supplement its water supply. But these are regional measures and provide little help elsewhere.
The problem is particularly bad in the U.S., where we use twice the amount of water on a per capita basis than the rest of the world. Florida will soon feel the pinch. The Environmental Protection Agency says we will need to spend $16.5 billion over the next twenty years just to maintain our current drinking water infrastructure. Even with that funding, the state will face a billiongallon-a-day freshwater shortfall by 2030. Many shallow aquifers are already tapped out.
In Collier County, water usage is expected to jump from 45 million gallons a day to 60 million or more by the 2030s. Even with aggressive recycling, we face a serious shortfall. The good news is we can deal with it. Although groundwater supplies are shrinking, Florida has seawater on three sides and humid air overhead.
Water from both can be captured and purified. Some of the technology to do that – distillation and reverse osmosis – is well established, while other methods are relatively new. The most exciting advance is squeezing water from the atmosphere – harvesting the moisture that surrounds us.
Chemical & Engineering News reports on vapor condensation on fine mesh surfaces with openings optimized to trap and drain the droplets. Another approach uses hydrophilic coatings on nonwoven fabrics of the type used to make dust masks. Still another uses tiles resembling layered fir cones, with optimized angles and pore sizes to collect and channel the moisture.
Since these systems don’t need an energy source, they can be set up anywhere and should be useful in high-humidity areas like Florida. In more arid climes, a better approach is a module that actually condenses the vapor like a dehumidifier. Such systems pull in air through an electrostatic filter to remove dust and other particles, then condense the vapors and pass the stream through a carbon filter and mineral cartridge to make the water drinkable.
Other variants are being developed. Researchers at MIT and Cal-Berkeley are crafting devices that use desiccants to pull water from the air, moisture-absorbing chemicals that give back water when heated by sunlight – an ideal system for the desert. The kicker, of course, is that none of this is free. Even reverse osmosis, a cheap form of desalting, can nearly double the cost of drinking water.
So while there may be plenty of water around (70% of the earth’s surface is covered by ocean), cheap, plentiful freshwater will soon be a thing of the past. The operable word is cheap. Before long we will have to pay a great deal more for the drinking water we take for granted today. But don’t give up on technology. There may still be way to have it all.
The U.S. Department of Energy is working on a wave-driven converter to power RO desalination at the seashore. How about that? Water using its own energy to desalt itself.
Water purifying water!