The last and most polluting procedure is washing the jeans, which determines their shade.

Today's trends include stone wash, enzyme wash, sand wash, chemical wash, bleach wash, destroy wash and snow wash jeans.

But none of these looks can be achieved without a strong base, strong oxidants and other chemicals, such as potassium permanganate, that can harm human health and the environment.

It is estimated that 20 washing factories operate in Fumian, processing more than 600,000 pairs of jeans each day at a cost of about one yuan per pair.

Yet the environmental cost is much higher because of the wastewater discharged by the factories.

"Most of the factories did no processing of wastewater until 2005, when the government launched a campaign to tackle the pollution," a local official said.

But local residents, some of whom used to work in the washing factories, said the so-called processing facilities were basically just a concrete settling pond.

"The smelly water they discharge is not dark as ink, as before. But I am sure the damage the water does to humans and the environment is no less than before," said one resident, who asked to remain anonymous.

The water quality of the three local rivers of Nanliu, Beiliu and Jiuzhou has not improved much since becoming contaminated in the mid-1990s. The towns and counties in the region, include Fumian, did not begin building sewage disposal plants until just a few years ago, and some have not functioned until recently.

Chen Guonan, a retired local geologist in his 80s, was the only local expert willing to go on the record.

"The local granite is very young, making the local groundwater the best in China. But the washing factories' sewage destroys it all. If no more pollution occurs from now on, it would still take half a century for the groundwater to purify itself," he said.

The washing factories work mainly at night after the jeans factories send them their finished products.

But local residents believe that they work at night to evade the environmental authority's supervision.