Will There Always be Water When You Turn on the Tap?

Most people in rich countries and even in cities of developing nations expect water routinely to come out of the tap in their house or yard. But with a population growing faster than the water supply, will that always be true? An article in Nature News this week offers a few possibilities for trying to squeeze more fresh water out of a thirsty planet. They discuss five options:

1. Desalination is very expensive, but if you can afford it, it can work: 

A rapidly growing global industry, desalination has become in the past 20 years an essential source of fresh water for the Middle East, Australia, the United States, South Africa, Spain and, increasingly, India and China. In 2012, the total amount of installed desalination capacity exceeded 80 million cubic metres per day, enough to supply some 200 million people.

2. Riverbank filtration is, I admit, a new one to me although it seems quite straightforward:

The method is straightforward: when wells are dug next to a river in regions with suitable geology, the river water filters through sand and gravel that strips out most of the chemical and biological pollutants, and so emerges relatively clean.

3. Water storage--new tricks on an ancient idea:

“Water scarcity is often caused by sporadic rainfall rather than actual lack of water,” says Alberto Montanari, a hydrologist at the University of Bologna in Italy. “The challenge then is to devise sustainable solutions for storing water to make a reserve for the dry season.

4. Greenhouses in the desert (as long as that desert is by the ocean):

Greenhouses normally trap heat, but the reverse is required in hot places such as Qatar. At the SFP facility, sea water does the trick. The water, piped from the ocean just 100 metres away, trickles over a lattice at the windward side of the greenhouse. As the water evaporates, it humidifies the air entering the greenhouse and cools it by some 10 °C, creating an indoor climate suitable for growing vegetables such as cucumbers and tomatoes. Other crops, such as barley, salad rocket and useful desert plants, grow between hedges downwind of the greenhouse.

5. Harvesting the fog (I'm not making this up):

Fog collection is catching on in seasonally dry regions that lack other sources of fresh water. The first simple mesh panels were built in the 1960s in the port town of Antofagasta in northern Chile. Today, 35 countries are using the technique, particularly along the Pacific coast of South and Central America, in the Atlas Mountains in Morocco and on the high plateaux of Eritrea and Nepal. 

None of these methods, in and of themselves, will solve the water shortage problem, but the article starts out with the information that the government of Iran is looking for any way to save and reuse water, as are many other countries:

From the southwest United States to southern Spain and northern China, water shortages threaten many parts of the world. Nearly 800 million people lack access to safe drinking water and 2.5 billion have no proper sanitation.

The situation will probably get worse in coming decades. The world's population is expected to swell from 7 billion today to more than 9 billion by 2050, even as climate change robs precipitation from many parched parts of the planet. If the world warms by just 2 °C above the present level by the end of the century, which scientists believe is exceedingly likely, up to one-fifth of the global population could suffer severe shortages of fresh water.