People would be forgiven for wondering why “rainy London” has just got a brand-new desalination plant, something more commonly associated with the sun-scorched Middle East or southern Spain.
Well, “rainy” London is less rainy than you might at first think. It gets half as much rain as Sydney, and less than sun-baked Istanbul or Dallas.
In fact, the capital is deemed “seriously water-stressed” by the Environment Agency, which means demand risks outpacing supply. And London running short of water definitely isn’t in Thames Water’s plan.
It wasn’t that long ago that London was in a drought. Issuing hosepipe bans in 2005/06 while leakage spiralled was, understandably, not received well. Only a very wet May saved the day for Thames Water. It was too close for comfort, and we never want to go there again.
Since then Thames Water has cut leakage by 27%, hitting the regulator Ofwat’s target for the last four years running. Great progress, but still not enough to guarantee London has enough water to meet predicted future demand in a prolonged dry spell.
With climate change threatening hotter, drier summers, like the one we’re in now, and an additional 700,000 people predicted to move into London by 2021, new sources of water are needed.
Our ground and non-tidal river water sources are at their permitted abstraction limits, so taking more water out of rivers and boreholes simply isn’t an option. That’s why we’re tapping the new and seemingly limitless resource of the tidal River Thames.
The £270m Thames Gateway Water Treatment Works, at Beckton in east London, will, when needed, be able to provide an additional 150 million litres a day, enough for one million Londoners.
This state-of-the-art new works, mainland UK’s first large-scale desalination plant, won’t run all the time. We’ll turn it on only when we really need to, when we’re next in a drought.
And, thankfully, we’re not in a drought right now. Despite the driest start to a year since 1929 in the Northwest of England, the Thames Water region is in pretty good shape at the moment. Between May last year and June this year we had 99% of the long-term average rainfall for our region. And after two normal-to-wet winters and a wet summer in 2009, groundwater stocks are healthy and our reservoirs are full.
So although we’re not expecting to turn on the new plant any time soon, it’s good to be prepared if the situation changes. Security of our 8.5m customers’ water supply is, after all, our top priority – whatever the weather.
However, as a company aiming to cut its carbon footprint by 20% on 1990 levels by 2020, desalination was not an option chosen lightly. It is well-known that this process is more energy-intensive than traditional water treatment. Reverse osmosis, which involves forcing salty water through extremely fine membranes, is what sets desalination apart from traditional water treatment. It’s also what requires so much more energy.
We had a challenge on our hands: balancing the competing pressures of ensuring we can provide all our customers with safe, clean water in future – while treading as lightly as possible on the environment, which we depend on for our core business.
The result is arguably the greenest desalination plant in the world. While most reverse osmosis plants have one or two stages, which yield around half of the source water as drinking water, the Gateway works is the world’s first-ever four-stage reverse osmosis system, yielding a far more efficient 85%.
The plant, when it’s in use, will treat brackish water, a mixture of sea and fresh water from the tidal Thames – less salty and so requiring less energy to treat than straight seawater. Raw water will only go into the plant on the last three hours of the outgoing tide, when the mix of brackish water is predominantly river water, so less salty. Vast tanks, which pre-existed the new works, will then hold the water which will then be taken into the works to be treated.
The Gateway works will run on biodiesel, derived from sustainable materials including used cooking oil, which could otherwise end up down our sewers causing nasty blockages.
So fat from the local chippy will play its part in running on-site biodiesel generators, producing electricity to power the plant.
Steps have also been taken to ensure the local fish population is untroubled by the arrival of the new works. There is an acoustic fish deterrent at the intake point, where water from the tidal Thames is taken into the plant, sending out a high-pitched underwater noise, which drives small fish away so they don’t end up in water holding tanks.
Local ants have also been looked after. During the building of the £20m, 14km pipe to take treated water from the works to our supply network, around 300 ant hills were painstakingly moved and repositioned so the sun hits them from the same angle.
Ants, check. Fish, check. You get the point. The upshot is a back-up supply for when the next drought hits – in addition to our other activities to manage water resources, such as reducing leakage, fitting water meters and encouraging people to be more water-efficient.
Water is an increasingly precious resource, something even we Brits can no longer take for granted. And the new Gateway water works is proof of that – proof that “rainy London” is perhaps rainy only in name.