By Emma Graham-Harrison

YINGXIU, China, May 18 (Reuters) - There is water everywhere in China's quake-ravaged Sichuan province, where rain is hampering rescue efforts and reservoirs are pressing against weakened dams.

But for some people there is not a drop to drink.

As rescuers race against time to find people trapped in the rubble of Monday's earthquake, officials must also worry about supplying water to millions of people living in damaged towns or tent camps.

Water supply to the populous cities of Chengdu and Chongqing was largely unaffected by the 7.9-magnitude earthquake that struck a wide swathe of northern Sichuan on May 12.

But in smaller towns, like Yingxiu near the epicenter, unclean drinking water is a growing problem for locals and for the refugees trekking in from flattened villages up in the mountains.

In Yingxiu, accessible only by foot in the days after the quake, the only available bottled water appeared to be that scavenged from wrecked homes and hotels.

Troops involved in the rescue effort and quake survivors trekked up a small hill to bring down water from a mountain stream, which was boiled but not always for very long.

One group of school children left behind a large water barrel that a medic from Guangdong province rushed to collect.

"I'm sorry, but we didn't bring enough water for ourselves," she apologised as she rolled it away from a group of journalists.

So far, about 29,000 people have died in the quake, a grim toll that authorities fear could mount to 50,000 as rescuers reach cut-off towns.

DAMAGED PIPES

In badly-hit mid-sized cities like Mianzhu or Dujiangyan, pipe damage means that water supply for the short term will be irregular and pressure abnormal, Li Dongxu, head of urban construction for the Ministry of Housing and Urban-Rural Development, told reporters this week.

The public water system has been completely destroyed in Beichuan and Wenchuan, near the epicenter, he acknowledged.

Damaged irrigation systems means that some rice paddies in Sichuan will have to be shifted to dry fields, at least for this summer, the vice minister of agriculture said on Saturday.

The destruction of factories, small workshops and cars could add to the water problem, if spilled chemicals and motor fuel make their way into streams and rivers, said Ma Jun, director of the Institute of Public and Environmental Affairs, which monitors water and air pollution.

So far, that hasn't happened, at least in the Min River system, which runs through the epicenter to Dujiangyan, said Samantha Bowles, spokeswoman for Veolia, whose plant supplies drinking water to one-third of Chengdu's residents.

But turbidity, or the amount of dirt and rocks in the water, has "dramatically increased," she said.

For the moment, an outpouring of donations and deliveries by people across China has ensured bottled drinking water is no longer a problem in areas accessible by road.

Once roads open, the army can also bring in water purefying machines or tablets.

In Dujiangyan, the site of one of the world's oldest flood control systems, tankers truck in water, although not everyone trusts it. People fill buckets and kettles at fire hydrants.

"I only use that for cooking because I'm not sure its clean. I got someone coming from Chengdu to bring us bottled water to drink," said one woman, who braved the risk of aftershocks to stay in her two-storey home.

"We can't wash ourselves though, only sponge ourselves down with a cloth," she added -- a common complaint among survivors. (Additional reporting and writing by Lucy Hornby; Editing by Sanjeev Miglani)

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