In the second in our series of days out ideas for the summer, Prof Ged Martin looks at the background to England’s 11th largest reservoir

We often complain that Britain lacks joined-up planning. In the decades after the Second World War, thousands of houses were built across Havering - but nobody seemed to realise that more people meant more sewage.

Result? By the 1960s, Elm Park's Bretons sewage works was overloaded - and very smelly. It was eventually replaced in 1968, and is now an outdoor centre.

But two public utilities had the foresight to provide water for the growing population of Essex (Havering included).

Britain was still recovering from six years of war when South Essex Waterworks and the Southend Waterworks Company announced their big project in January 1949.

South Essex Waterworks had been supplying Romford since 1863. Much of its water came from deep underground: there was an artesian well in South Street, opposite Clydesdale Road.

But the companies believed existing supplies were "insufficient to meet the demands of the growing population".

Two big housing projects in particular needed fresh supplies: Basildon New Town and Harold Hill.

Almost 1,000 acres of land would be flooded to form a reservoir between the villages of West and South Hanningfield. Water would be pumped from the Chelmer and Blackwater, reducing the risk of flooding from those rivers.

It's a slander that Essex is flat, but the saucer-shaped valley of the Sandon Brook did require one of the biggest earth dams in Europe to create adequate storage. A mile and a quarter long, it's a bit disappointing as there are no views over the reservoir.

It was a surprisingly empty area, with just a few farms and one tiny hamlet. The complication was an ancient gabled mansion called Fremnells, once the home of Oliver Cromwell's brother-in-law.

A couple of dotty attempts were made to block the project in the House of Lords. "Water is an intractable material," the Earl of Radnor pronounced in 1949. "It cannot be stored on top of a hill, as it has a habit of running down."

He objected to swamping valuable farmland. Couldn't they build reservoirs in places like in Wales and Dartmoor, and pipe the water across country to Essex? (Answer: No, Your Lordship.)

In 1951, Viscount Esher made a last-ditch attempt to save the "charming and interesting" Fremnells by constructing a much smaller reservoir, with a second dam to protect the mansion.

Government spokespersons sweetly replied that Fremnells was a nice old house but not very special. It was demolished. Sadly, nobody suggested rebuilding it somewhere else.

It's a good job planning started so soon after the war, as the reservoir took five years to construct and only began operating in 1957. Remarkably, it cost just £6million.

All existing buildings were cleared. Unlike reservoirs in Wales and the North, no ghost settlements would re-emerge in drought years.

Hanningfield Reservoir is six miles in circumference, and its deepest point is 16.76 metres (about 55 feet) - Essex isn't so flat after all. It contains 26 billion litres of water, equal to 10,000 Olympic swimming pools. The reservoir took 200 days to fill. By coincidence, it contains enough water for 200 days supply, providing 150 million litres to half a million homes every day.

In 2000 the Essex Wildlife Trust opened a visitor centre, complete with a cafe. Its 100-acre nature reserve is popular with bird watchers: Hanningfield is a special place for ducks. The reservoir is also popular with anglers, with facilities at the nearby Waterside Park.

Hanningfield reservoir, now run by Essex and Suffolk Water, is mysteriously tucked away. Driving from Havering, take the B1007 through Billericay. Half a mile beyond Stock, look for the brown tourist sign pointing right along Downham Road. Hawkswood Road, also signposted, turns left after about a mile. Near the visitor centre, there's a fine view over the reservoir - you could almost be in Canada. Dogs and smoking are banned. Visitors are asked for a donation.