DEMAND FIVE

Almost twice the length of the Channel Tunnel, the Thames Water Ring Main is a hidden engineering marvel. Each day it carries a billion litres of liquid, keeping millions of homes supplied with fresh tap water. Robert descends 40 metres underground to witness the work of the tunnel boring machine that is slowly extending the ring main at a rate of about 30 metres a day. The tunnellers have to steer the giant contraption to create a gentle downhill gradient from the reservoirs to the city centre, since the whole system relies on gravity alone to keep the water moving.

On the edge of the Mojave Desert in California, the blades of over 5,000 wind turbines sweep rhythmically through the air. Owing to a steady wind flow in the area, the Tehachapi Mountains overlooking the desert are home to one of the largest wind farms in the world. The farm generates almost one and a half billion kilowatt hours of electricity a year – enough to supply more than 75,000 homes. But the wind turbines have one big enemy – flies. Every day, hundreds of insects are swatted by the revolving blades, and as the resultant debris builds up, the windmills become less and less efficient. Since the Mojave is one of the driest places on Earth, the turbine operators have to create their own rain to wash the dead flies away...

Staying in North America, Robert’s final voyage of discovery this week takes him into the world of ice hockey. In this part of the world, the sport is immensely popular and is supported by a multi­billion dollar industry. But every 20 minutes during every game, the action halts as the ice is resurfaced. The Zamboni company has been making ice-resurfacing machines for over 50 years. The secret of this unlikely sporting icon’s success is that it not only shaves off the scratched and pitted ice, but in the same movement lays down a new, slippery smooth surface, allowing play to carry on after the shortest of breaks.

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