A spectacular piece of engineering history is open to the public for the first time this year over the Bank Holiday, and it features a new guide book. Chris Lloyd reports

THERE’S a subterranean rhythmic rumble which is accompanied by a trebly hiss of escaping steam on the off-beat, but the machinery itself moves noiselessly from floor to ceiling, from way overhead to deep down below. The governor twirls like a ballerina performing an endless pirouette, while the 17-ton beam hypnotically nods backwards and forward, backwards and forwards, as it did in the days when it pumped clean water to the people of Darlington and the Tees Valley.

This weekend, the Tees Cottage Pumping Station, featuring its fabulous 1904 beam engine, is open to the public for the first time this year, and on sale for the first time will be a new guidebook, explaining the mechanical marvels that are in front of visitors’ eyes and the historical stories that lie behind them.

The site at Broken Scar is a Scheduled Ancient Monument, and as well as including the largest, fully operational historic gas engine in Europe, it contains a flood of stories of alleged corruption, of “profound sewage contamination” and, on the plus side, of extremely tasty beer.

There was great concern about water quality 170 years ago as science was beginning to explain water-borne diseases like cholera. In Darlington, 1,470 houses got their water from 19 public wells. Livestock milled incontinently around the wellheads, particularly on market day, while other wells had been sunk distressingly close to burial grounds.

Some houses got their water from butts, which were no more hygienic – in 1851, a doctor supervised the emptying of a waterbutt in a yard in Bondgate and found at the bottom the decomposing body of a baby. He reckoned the inhabitants of the yard had been drinking the water for at least six months.

So in 1849, the three sons of Edward “the father of the railways” Pease formed the Darlington Gas and Water Company: John chaired it, Joseph was the principal shareholder and Henry was the managing director.

The idea was to pump water out of the River Tees, clean it, and then let it flow into the homes of subscribers. The Peases called in Thomas Hawksley from Nottingham, the greatest water engineer of his day, to design a system. He estimated it would cost them £13,000 to build but would return a healthy profit of £843-a-year.

On Wednesday, April 24, 1850, Edward Pease wrote in his diary: "There was considerable stir in Darlington today, this being the first day water was brought into the town from the New Water Works."

The water and had “the colour of India Pale Ale and a slight taste of pond”, and its arrival created a sceptical stir. Old farmers knew that cows that grazed beside the Tees suffered from diseased lungs and became "belloned" – or short-winded – and old anglers knew that the fish in the Tees were poisoned by lead from the mines up the dale.

Because of the scepticism, in the first year, there were only 230 paying customers. The charge was based on the rental value of a customer’s property: houses worth less than £3-a-year were charged 1d-per-week for water; those worth £100 or more paid 15s-per-quarter, and extra for “each water closet or immersion bath”.

But the first water drinkers did not die in droves. Instead they reported that “the beer was better and the tea stronger”. Subscribers began signing up, and the mains were extended into Stockton, Middlesbrough and Yarm, which were supplied by a second beam engine from September 1853.

In 1854, the Darlington Board of Health – the first vaguely democratic council – agreed to take the water company into public ownership. The Board, which was chaired by Joseph Pease and included his two brothers, agreed to buy the water company for £54,000 – about twice what the Peases had invested in it just five years earlier.

Critics accused the Peases of “unbridled profiteering”, and the Northern Daily Express said with incredulity: “The gentlemen who were acting for the ratepayers were precisely the same gentlemen who were bargaining for themselves.”

Demand for water rapidly grew as population exploded. In 1860, the Darlington side of the operation took over the whole of the pumping station while the Teesside arm was moved across Coniscliffe Road.

Yet in the early 1890s, the initial doubters must have felt themselves vindicated because there were two typhoid outbreaks among the water board’s customers, causing 24 to die in Darlington alone.

Barnard Castle was to blame. Inspectors found the river to be full of “black stinking…excremental filth”, and described how the “washings of highly manured lands, drainage of graveyards and farmhouses, of privies, urinals, waterclosets along the foreshore, of loads of stinking refuse, ashes, midden refuse, gasworks refuse and other accumulations of filth” all ended up in the river. They even noted how the infections broke out immediately after a summer flood had washed through Barney, clearing out all the faeces which had been baking for months on the riverbank beneath the houses.

The town was ordered to clean up its act with a sewage works, and the Teesside water board began to build reservoirs in the Pennines to bypass Barney.

The river clean-up worked for Darlington, and with confidence in the water restored, in 1902-04, Tees Cottage embarked on a £21,490 investment programme, overseen by Hawksley’s but carried out by Teasdale Brothers.

Brothers John and Robert Teasdale had formed their company in Burneston, near Bedale, in the 1820s, to make agricultural equipment like root cutters and turnip toppers. They moved to Bank Top in Darlington in the 1870s, and from their agricultural base made forays into big projects: in 1895, they built the Stone Bridge beneath St Cuthbert’s Church which still bears their name, and in 1902 they built the two huge boilers at Tees Cottage.

Then in 1904, they installed the magnificent beam engine – designed in Kilmarnock but perhaps built in Leeds or Manchester – which is driven by the boilers. This was one of the last steam-driven pumping engines installed anywhere in the country, before electricity took over, and it represents this old technology at its most efficient and impressive. It is housed in a cathedral-like building that is full of municipal pride and craftsmanship.

The engine pumped 1,900 gallons of water-a-minute out of the Tees and into the filtration tanks. It then pumped 1,800 gallons to customers, so it moved a total of 2.4m gallons a day.

It had a voracious appetite: its boilers required 30 tons of coal a week, or six wagonloads a day, delivered from the railway siding at Merrybent, which meant the unfortunate boilerman shovelled four tons of coal a day.

It worked without a hitch until 1926 new technology took over. Electric pumps were installed to take on the bulk of the work and the old “slow sand filters”, which relied on natural bacterial work to clean the water, were replaced by a quicker, chemical treatment works over the road in what is now the Northumbrian Water site.

The beam engine was kept for back-up and was operational until 1980, when Northumbrian Water’s new Broken Scar works opened over the road.

Since then, it has undergone many restorations and, staffed by volunteers, is open five time a year. The first openings this year are on Sunday and Monday, from 11am to 4pm, admission £5, when the new, bite-sized guidebook will be on sale for £2.50.