Teach a man to fish - and you feed him for life. That's a nice saying, but soon you won't be able to feed this man in developing countries. That's not only because there are fewer fish but also less, or even no, water.
Hong Kong had water rationing from the 1960s until the 1980s, when we negotiated a deal with the mainland to import water from the Dongjiang, or East River.
Although 'no-water' days seem quite distant in Hong Kong, in some parts of the world such as North Africa, Central Asia and the Middle East, they are just another regular day.
One-fifth of the human race suffers from water scarcity, while a further one-fifth does not have clean water. This shows the extent of the problem, particularly in the developing world.
The problem is caused by extended droughts, rising agricultural demand, dams in the upper reaches of rivers, pollution and, most importantly, the growing world population.
If you think the only victims of the water crisis are humans, you are wrong. An international research partnership recently reported in the journal Nature that no fewer than 10,000 freshwater species are estimated to have become extinct or are at risk of becoming extinct.