Image caption The San Francisco Peaks are a beautiful hike for some, a good ski slope for others, and a sacred entity to the Hopi Indians

A ski area in the US state of Arizona hopes to become the latest in a small number of resorts using "recycled" sewer water to make snow. But the Hopi Indian tribe aims to stop what they describe as the desecration of their sacred mountain.

The San Francisco Peaks tower over the baking Arizona desert. Stands of white barked aspens, spruce and ponderosa pines dot the high tundra landscape, and the mountain is the highest in the state.

The US Forest Service, which manages the land, recommends it for hikers seeking solitude in the wilderness. The mountain is a holy entity for the Hopi and other Indian tribes who lived in the area centuries before Europeans arrived.

On the mountain's western face lies the Arizona Snowbowl ski resort, a narrow 777-acre block of land poking 10,000ft (3,048m) into the wilderness area, which surrounds it on three sides.

People have been skiing there since 1938. But Arizona is one of the driest states in the US, and a recent run of dry winters has left the operators scrambling to find water to make artificial snow to keep skiers - and their dollars - on the slopes.

Image caption Hopi Chairman LeRoy Shingoitewa fears the recycled water would "defile" the mountain

The resort's owners, who manage the resort under an agreement with the US government, are embroiled in a row with the Hopi Indian tribe, which has filed a lawsuit to stop Snowbowl's plan to pump highly treated wastewater from the nearby city of Flagstaff up the ski runs to make artificial snow.

The Hopi say spraying treated wastewater on the mountain - even just within the boundaries of the ski resort - would irreparably sully it and threaten their ability to carry out their religious rites among the peaks. And they say it would defile the pristine wilderness for all those who want to enjoy it without skies on.

"The Hopi people believe it is up to moisture from the sky to bring in water," says LeRoy Shingoitewa, Hopi tribal chairman and a former school principal.

"We believe that whatever comes off the mountain is pure. When you take something that is not pure and defile it, it becomes a dirty object. Would you use something in your ceremony that is not clean?"

'Less financial uncertainty'

The Hopi and other Indian groups in the area have been battling the ski resort for decades, but the recent row began in 2002, when the ski area asked the Forest Service for permission to add a new ski lift and carve new ski trails and to buy up to 1.5m US gallons (5.7m litres) of treated sewage a day from Flagstaff during ski season for snow making.

"Snow making is the only viable method to ensure consistent and reliable operating season each year with more stable visitor use and less financial uncertainty," Ed Borowsky, one of the owners of the Snowbowl, wrote in a sworn affidavit in federal court.

Image caption Snowbowl owners hope to extend the resort's short ski season in dry years

The operators also found that recycled sewage was the only available water source in the dry desert region.

"No matter how deep you dig, it is impossible to predict whether you will get a dry hole, a slow trickle, or whether you will truly strike water," Mr Borowsky wrote.

Snowbowl officials did not respond to interview requests, and Flagstaff declined to make officials available.

The Forest Service and later the federal courts dismissed the Indian tribes' opposition and allowed the Snowbowl expansion to begin. But this summer, the Hopi tried a new legal tactic. In a state court, they claim Snowbowl's contract to buy Flagstaff's treated wastewater violates state environmental law and ask it be voided.

In the US and across the world, recycled sewage has for decades been used in a variety of applications in which it does not come into sustained contact with humans.

Conserving water

The stringency of treatment the wastewater undergoes depends on its ultimate use.

Recycled water use across the globe Namibia: In the capital Windhoek, highly treated wastewater is reused as drinking water - the only example of direct reuse in the world

In the capital Windhoek, highly treated wastewater is reused as drinking water - the only example of direct reuse in the world Australia: Variety of uses, including ski snow making, residential toilet flushing and crop irrigation

Variety of uses, including ski snow making, residential toilet flushing and crop irrigation Japan: Irrigation of parks, golf courses, sport pitches; road cleaning, car washing, firefighting, on-site reuse in commercial and residential buildings

Irrigation of parks, golf courses, sport pitches; road cleaning, car washing, firefighting, on-site reuse in commercial and residential buildings UK: Treated wastewater used for fish farming, car washes, and golf course irrigation and the Millennium Dome in London reuses treated wastewater in toilets and urinals

Treated wastewater used for fish farming, car washes, and golf course irrigation and the Millennium Dome in London reuses treated wastewater in toilets and urinals Pakistan: Untreated wastewater irrigates vegetables, livestock fodder and wheat Sources: US Environmental Protection Agency, BBC research

It can be filtered several times, zapped with ultraviolet lights, injected with chlorine and allowed to settle for long periods. It is used in golf course and park irrigation, car washes, firefighting, industrial applications, irrigation of some crops, and in toilets in commercial buildings. Except in the city of Windhoek, Namibia in Africa, it is not drunk, people familiar with the industry say. Nor is it used in swimming pools.

Recycled water advocates describe it as a process that is ultimately beneficial to the environment, because it conserves a precious natural resource like recycling newspapers saves trees.

"If one uses recycled water, you're taking pressure off of the [drinkable] water supply," says Wade Miller, executive director of the WateReuse Association, a US non-profit advocacy and lobbying organisation.

"If you're using water more than once, you're reducing your water footprint and you're reducing your energy footprint."

It is unclear how many of the more than 480 ski areas in the US use recycled wastewater in snow making operations, though the number is miniscule.

Seven Springs Mountain Resort in Pennsylvania uses diluted recycled wastewater to augment the collected surface water it uses to make snow, says Chris Marso, the executive director of operations.

"It's been treated, it's filtered," he says. "It's probably better than the pond water."

Bear Creek Mountain Resort, also in Pennsylvania, hopes to begin using recycled wastewater to make ski snow this season, in a nine to one ratio with untreated fresh water, says Mark Schroetel, the resort's general manager.

"It's a resource that we have at our disposal to use," Mr Schroetel says. "Water is at a premium. Any water we can get a hold of is added security for us."

And at least two ski resorts in Australia - a continent devastated by prolonged drought - make snow from recycled wastewater.

The recycled water taken from Flagstaff won't smell and it won't be cloudy, supporters say, but a previous US Geological Survey study has found trace amounts of some common pharmaceutical chemicals, caffeine, cleaning products, sunscreen agents and other household and industrial chemicals.

Water reuse advocates say the amounts are so miniscule as to be harmless in casual exposure.

But the Hopi fear spraying the water on the San Francisco Peaks will do lasting damage to the ecosystem there, and they are unconvinced by the science.

The tribe, in its capacity as a taxpayer and property owner in the city of Flagstaff, has sued the city to stop it from selling the water to the Snowbowl. It says that use of the water would violate state environmental laws, though the regulations expressly allow use in snow making.

"What does clean mean?" asks Mr Shingoitewa. "The more we looked at it, the more we were told by our people, you've got to protect that sacred mountain."