The emergency water unit being loaded on to a truck in Sandaoyan can't come fast enough for earthquake refugees in Xiang'e, 30 km and one nightmare away.

The 5 million people left homeless after Sichuan's 7.9-magnitude earthquake on May 12 have been liberally supplied with bottled water by the military and by thousands of volunteers who raced to help.

But drinking water remains a long-term problem for Xiang'e and for China's entire massive relief effort, which will last for months. Clean water is essential for preventing disease and for the daily comfort of refugees, most of whom haven't showered since the earthquake upended their world.

"China's government is now worrying about a few epidemics like hepatitis, plague, meningitis," said Anne de Bagneux, managing director for central China for Veolia Water, a unit of Veolia Environment that provides clean water to one-third of Sichuan's capital, Chengdu.

"Water can convey these kinds of epidemics, so it's quite dangerous in these circumstances, after an earthquake, to drink untreated water."

Veolia Force, the company's emergency response unit, has donated two units to Sichuan that can provide treated water to 5,000 people each. One of the units rolled out on Thursday to Xiang'e, where townspeople living under tarpaulins and tents have depleted a muddy stream.

For the long term, China will need hundreds more such units to supply clean water on a regular basis. Sites have to be chosen based on availability of water and accessibility for the people using it.

The earthquake disrupted river beds, making water murkier than usual, and the millions of people in tent camps means the country has to carefully control sewage and sanitation.

"For drinking we have bottled water. And the army gave us some that they say we can use once it has settled," said Liu Dayong, who with her family was camping out in a filthy scrap metal yard next to her former home in Xiang'e.

"For washing and things like brushing teeth, we use the stream. It's only a mouthful, and we are careful not to swallow. Don't even mention a shower."

Xiang'e benefits from its closeness to Chengdu. Volunteers keep the town well stocked with rice, potatoes, soy sauce and vegetables, whereas refugees further out rely on a daily diet of instant noodles and biscuits.

For the time being, until the water unit is set up, that means people have plenty to drink but not much to use otherwise.

"Budweiser came by today and gave us more bottled water than we know what to do with," said Li Rong, trying to hand a bottle to a reporter.