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.
Sadly, costly engineering "solutions" pursued by wealthy countries could improve water usage efficiency. But they fail to address the roots of the problem - mismanagement of freshwater resources and inadequate biodiversity conservation.
Protecting catchment areas and re-engineering large dams appear to offer even developing countries less expensive ways to overcome a water shortage. The need for such management measures may become more urgent in light of more chronic droughts in areas already lacking water because of climate change and escalating demand from the ballooning population.
And that brings the issue back to Guangdong and Hong Kong. Water supply here is secure as it is prioritised within the Pearl River Delta.
But there is no reason why high-volume users should not be charged more. It would be an incentive not to waste water.
Conservation is what matters most. To teach a man to fish, all species, and water itself, must be conserved in the first place.