They look like a staircase for giants. But these stone-walled steps down a mountainside in the Philippines are actually narrow fields where farmers grow rice. And each step is kept watered by a complicated network of channels that takes water on to each terrace, starting from a spring near the top. This brilliant engineering – seen here at Banaue where the terraces have been declared a World Heritage Site – creates fertile land out of steep slopes. The first terraces were built on Luzon by the Ifugao people around 2 000 years ago. That was when the Romans were building their water aqueducts in Europe. But, unlike Roman waterworks, the terraces remain in use, constantly maintained and extended by the Ifugao farmers of today.
PHOTO: ROMY HITOSIS/UNEP/B

Lake Baikal, in the middle of Siberia, is the oldest and largest body of freshwater on the planet. It is 25 million years old, over 600 kilometres long and in places 1.6 kilometres deep – almost as deep as the oceans. The lake contains a fifth of all the liquid freshwater on the planet. It would take all the rivers of the world a year to fill it. And the lake, a World Heritage Site, is home to an amazing 1 200 species of plants, animals and fish found nowhere else on Earth, including its own unique seal.
PHOTO: K TEULING/UNEP/TOPHAM

The Sahara may be a desert today, but once it was wet. And underneath it still lie huge amounts of water. Most of it is 30 000 years old. For the last 10 years, Libya has been pumping this water up from hundreds of wells sunk into the desert sands, and sending it in huge pipes to farms on the distant coast. The pipes are so big you could drive a truck through them. And they carry as much water as a river like the Mersey in England or the Rio Grande in America. In fact, this is Libya’s only river.
PHOTO: LUCA ZAVETTI/LOOKAT

Jimmy Angel found the Angel Falls deep in the Devil’s Canyon in the rainforests of Venezuela back in 1933. He was looking for gold, but instead found the world’s tallest waterfall. It is almost a kilometre high, falling straight off Auyan Tepui mountain into the jungle below. Of course the local Indians, the Pemones people, knew about the falls long before Jimmy Angel flew his bush plane down the canyon and saw it. They called it the Churún Merú. But Jimmy told the rest of the world so it bears his name.
PHOTO: COURTNEY MILNE

The Sudd marshes are the biggest inland wetland in the world. Their lakes and swaying papyrus cover an area bigger than England and are home to elephants, hippos, crocodiles, giraffes, antelope and millions of birds. The marshes get their water from the Nile, the world’s longest river. In fact, more than half the river’s water evaporates during its journey through the marshes. People downstream think that is a waste of water. Egypt and Sudan had a plan to dig a canal round the edge of Sudd, so the Nile could bypass the marshes. That way more water would be left to irrigate fields and fill taps. A civil war in Sudan stopped the canal when it was half-dug. But if it is ever completed, the great Sudd marshes would dry up.
PHOTO: MICHEL TERRETTAZ/WWF CANON