Water has always been the essential as well as the symbolic link between Hong Kong and the mainland. The arrangement has worked well until recent years, when changing circumstances made it something that was less of a bargain.
Now the SAR is reunited with China, and plans are in hand to forge closer links with special economic zones across the border, it is entirely appropriate the first fruits of this partnership should come from a mutually beneficial agreement affecting the water supply.
The plan to give an interest free loan to the Guangdong Provincial People's Government signals a new chapter of co-operation between the two authorities. It is likely to be the forerunner of many other technical advances and infrastructure projects.
Better still, the scheme promises much needed environmental benefits. That is perhaps the most important factor in the whole agreement, although a previous proposal to tap into the river further upstream where it is much purer has come to nothing.
The huge costs and the difficult engineering problems that such a scheme would present perhaps proved insurmountable.
Ecologists have expressed concern about the quality of the Dongjiang water as the area has become more populated, claiming there has been a massive increase in pesticides and heavy metals flowing into the river. Officials deny this, but they admit raw sewage has been finding its way into the supply, and it is obviously a matter of some urgency to upgrade the present quality.
The existing contract requires Hong Kong to pay a fixed sum for the supply, whether it is needed or not. Last year, when rainfall broke all records, and reservoirs were overflowing, Hong Kong was paying for water which went down the drain.
The mass migration of industry across the border means that the SAR uses much less water. That industry has also contributed to the pollution in the existing open aqueduct system. That statistic makes the plan to lend $2.3 billion to construct a closed aqueduct from Dongjiang cost effective. It would take a vastly greater sum to build reservoirs in Hong Kong, and lower bills will save the Government $2.2 billion over the next seven years.