China's per capita water reserves are only about one quarter of the global average. Of 670 of its major cities, 440 regularly suffer moderate to serious water shortages. Droughts have been the order of the day in the past few years, not only in the north and southwest of the country, but even in the relatively water-rich Guangdong province.
Hong Kong gets most of its water from north of the border. Hence, as the mainland's water reserves dwindle, will Hong Kong also face serious water shortages in a very short time?
'As the population grows and industry develops, demand is rapidly increasing in the Guangdong area. Critical times [such as droughts] will threaten both the quality and the quantity of water,' said Professor Joseph Lee Hun-wei of the University of Hong Kong's department of civil engineering.
The government has secured about 80 per cent of water supplies from Guangdong's Dongjiang river. It is some 80 kilometres north of Hong Kong, and provides about 20 per cent of the one billion cubic metres of drinking water we consume a year from locally-built dams and catchment areas. But several problems threaten the water supply.
'We cannot look at Hong Kong alone, it's an integrated system,' said Lee. '[The mainland's] improper land use, deforestation, intense urbanisation, soil erosion and pollution will result in poor water quality. They have an accumulative impact.'
Pollution of water catchment areas is a huge problem. This is caused by urbanisation and industrialisation, conservationists say. But according to Wen Tiejun, head of the school of agricultural economics and rural development at Renmin University of China, agriculture is the largest polluter with about 10 million tonnes of fertilisers finding their way into the country's waterways every year.
'The main problem is the big cities,' said Professor Ho Kin-chung, dean of the school of science and technology at The Open University of Hong Kong. 'The growth of water consumption is connected with GDP [growth], as economic activities increase and people find water more affordable.'
He said that in Hong Kong a household uses 120 litres of water a day - for Guangzhou the figure is 110 litres, for the Pearl River Delta it is 90 and for the whole of China it is only 45. Although the world's population only doubled in the past 50 years, its consumption of water tripled, while global GDP has grown 10-fold.
In Hong Kong, the growing population and an ageing water distribution system are putting a strain on supplies, with about 20 per cent of the water supply simply leaking away.
According to Ho, the government's HK$19 billion overhaul is on schedule and has already cut about 5 per cent of the leakage. However, this can only help to a certain extent because some of the leakage could be undetectable.
Also, leakage could be due to illegal use by construction companies, launderettes or barber shops. He said the international average of leakage in big cities was around 15 to 20 per cent and this was perfectly normal.
Ho believes our water supply from the mainland is secure until 2047, 50 years after the handover. He said: 'The supply of water is a political decision. Contracts [mean] nothing. Whether China would like to supply water to Hong Kong depends on whether Hong Kong is important to China.'
However, he agreed Hong Kong should take action to prevent water shortages by building more reservoirs, improving distribution, protecting the water resources and, most importantly, by early planning.
Lee said: 'There is no single solution, only an integrated solution that involves water treatment, public policy, recycling, desalination [and] water management.'
Read the other three parts of our bottled water series