Water companies were told by the NRA in June that it wants to set timetables to reduce abstractions from 40 rivers suffering from low flows.
The NRA approached Thames Water last year about the Darent problem, but was dissatisfied with the response and has now gone public with its demand for a voluntary cut in the company's abstractions in the area.
The Darent drains rolling countryside to the south-east of London. Before it reaches the Thames its modest flow is sucked into the chalk at Horton Kirby, south of Dartford. The catchment's problems are a textbook example of the failings in water resource management in the UK.
In 1945, the then Metropolitan Water Board drilled its first borehole in the valley to supply the growing population of south-east London. The number of boreholes and abstraction levels increased in the 1950s, although local residents were already complaining that private wells were drying up.
In 1963 the Water Resources Act introduced abstraction licensing. But due to pressure from the water supply industry, licences were not based on an assessment of the water resources but on the installed capacity of pumps. When a licence was granted for the Darent boreholes in 1966 the water board had installed a massive pumping capability of 90 megalitres/day. This was so far in excess of its requirements that it is doubtful that this amount has ever been abstracted.
A second blow to the river was dealt in 1985 when, in a remarkable act of short-sightedness, Thames Water Authority built a trunk sewer along the length of the catchment. The idea was to save the cost of sewage treatment in the Sevenoaks area by piping sewage to the bottom of the catchment, where a much greater flow was available to dilute discharges. As a result, all the water abstracted at Sevenoaks is permanently lost to the river. Now the Darent regularly dries out for a one or two mile stretch in its lower reaches.
Thames Water has sought to claim credit for limiting its abstraction in the valley to 70% of the licensed amount. Critics claim this was easy to do in view of the unrealistically large licensed quantity.
The NRA has now invited Thames to give its voluntary limit statutory force by applying to reduce the amount of its licence by 30% by 1 September. It is also being asked for a further 15% voluntary cut in its abstraction licence by the end of 1995. The NRA wants an answer by next April.
If Thames refuses, the NRA has said it will use its powers to vary the licence. The snag is that it would have to compensate the company for the loss of supply.
The capital cost of water is around £1.5 million per megalitre per day. A compensation claim could add up to about £25 million, plus legal costs, which the NRA would be forced to add to its water resources account.
The move would be certain to create more than a little tension in the water industry. The NRA's total expenditure on water resources was £75 million in 1991/2, but the bill for protecting the Darent would pass to its southern region.
The £25 million bill would therefore fall mainly on abstractors in the southern region, including Southern Water and several small statutory water companies, with only a modest proportion paid by Thames. Abstraction charges in the area currently raise only £6 million a year.
It would be small comfort for the customers of southern water companies, which already pay higher water costs than Thames Water's, that the situation arose through the mismanagement of Thames Water and its predecessors.
The choice facing the company is either to fund new resources to replace some of its Darent supply voluntarily, or else face the public relations nightmare of an open battle with the NRA and southern water abstractors, with the environmental lobby pitching in from the sides.
The NRA believes that the course of least resistance would be for Thames to include plans for replacing Darent supplies in its next five-year investment plan. But the company is resisting the very idea that its activities have any effect on the river. In a recent letter to The Times, Chief Executive Michael Hoffman claimed the state of the river was due to the drought.
The NRA's strategy is to keep a tight rein on water companies' resource policies, favouring investment in leakage control and metering over new reservoirs. Thames Water's approach in these areas may be causing it some concern.
The company gives its top managers incentives to boost sales of metered water. Its Chairman, Roy Watts, took a £15,000 cut in salary this year because metered water sales fell by 4%, mainly due to the recession.
The policy helps to explain Thames Water's bullish approach to its duty to supply and its eagerness to promise no hosepipe bans despite the drought. But it is unlikely to promote the sensible use of a finite resource, or encourage measures by consumers to conserve water.