Bali has a reputation as Indonesia's jewel island, attracting five million tourists each year. Volcanoes rise up from its interior, their slopes thick with rainforests. The coast is fringed with black sand beaches and coral reefs. But perhaps the island's most iconic view is the geometric patchwork of its verdant rice paddies.

For millennia, farmers have kept their paddies lush following the subak system of irrigation, recognized by UNESCO with a place on its World Heritage List.

I Wayan Gede Eka Sudiartha, a welder and part-time project manager at the Nyambu ecotourism village in Bali's Tabanan regency, demonstrates how farmers adjust hand-molded miniature mud dams each day to regulate a precise flow of water, which allows surplus to run into fields further down the luminous green steps. It's something they have done since the 9th century.

Traditionally, sowing and harvesting are staggered across different communities to balance out water use. In this way, the rainy season replenishes the aquifer with enough water to last all year, keeping the human population fed and allowing flora and fauna to flourish

Read More: Stopping India's water crisis

But tourism has thrown this carefully calibrated system out of whack. Over half of Bali's groundwater is consumed by the tourism industry, and there isn't enough to go round.

And a new development in Tabanan threatens to be the worst yet. The Trump International Hotel will include luxury villas and pools, as well as a vast, water-hogging golf course.

Irreversible damage

A partnership between the US president's hotel chain and Indonesian tycoon Hary Tanoesoedibjo, the project has angered locals for overshadowing Tanah Lot, the most important Hindu temple in Bali and a UNESCO World Heritage Site. According to local custom, no building should be higher than the tallest coconut palm, let alone tower above such an important spiritual site.

Trump Hotels didn't respond to DW inquiries as to whether it has any plans to minimize the development's impact on the environment and water supply.

Scientists at Bali's Denpasar Polytechnic say deep bore wells drilled by hotels, villa-based resorts and supporting industries, have already resulted in saltwater leaking into the groundwater. Once this happens, the damage is irreversible and farming, the lifeblood of the community, is at risk.

"I worry that if all the rice fields become [tourist] villas, what we will eat?" Sudiartha told DW. "We cannot eat money. We cannot eat concrete."

Komang Arya Ganaris is program manager of Bali Water Protection (BWP), a project of Balinese nongovernmental organization IDEP. He says there needs to be proper management of what should be an ample resource in Bali.

"We are a tropical island," Ganaris told DW. "How can we have a water crisis? We have a water management problem. There has been no monitoring of groundwater use."

Read more: Water: 'Era of stable abundance is over'

Revitalizing the wells

Simple technology could alleviate the problem, though. BWP wants to construct 136 "recharge," or gravity-fed, rain wells at strategic points across the island, following three years of research by Bali State Polytechnic.

The system has a proven track record in Afghanistan, Bangladesh and India, and a pilot for the scheme in Denpasar is already showing promising results. Local government is supporting the pilot with 100 million Indonesian rupiah (around €5,700, $6,500) a year, enough to fund just two or three wells.

To fund the entire Bali-wide project, BWP says it needs just $1 million — small change compared to the vast sums that flow through the island's tourism sector each year; the Trump resort alone is rumored to cost $1 billion.

But Ganaris says the Indonesian government won't fund the project without further evidence that it works. With time running out to save Bali's water supply, BWP is turning to crowdfunding, private donors, local communities and businesses.

Lilik Sudiajeng, the scientist in charge of the pilot in Denpasar, wrote in a report on the project that all new developments and even private households should have their own recharge wells.

Ganaris thinks the government also needs to put tariffs on water use by industries like tourism. "Industrial business is huge. We need big steps and big policies," he says.

Tourism in tune with tradition

Ib Putu Sunarbawa is chief of the Nyambu eco village. He told DW that tourism has become unmanageable. Unless Bali protects its unique landscapes and biodiversity, it's not just farming that will suffer. The natural beauty that draws tourists to the island will also be under threat. 

Read More: Bali takes on plastic pollution

But there are ways to enjoy the island's treasures without destroying them.

Nyambu is a traditional village of 3,700 people that has opened its gates to visitors. So far, three guides show tourists around its temples, homes and paddy fields. Each tree species has a special day and some trees wear sarongs since they house spirits. The villagers have built a bathing pool for monkeys and planted grapevines for them to eat from. Nature matters here.

"I want to care for the environment and develop the village," Sunarbawa says.

Sunarbawa would like to see the government limit the number of tourists on Bali, and offer only "quality" experiences like that at Nyambu — where tourists' money funds habitat maintenance for wildlife, extra income for families who offer homestay rooms in their traditional compounds and buys cultural experiences, like visits to many temples that honor water spirits.

Water has a central place in Balinese culture. A majority of Balinese follow a unique local brand of Hinduism, called Agama Tirta, meaning "the science of the holy water." Farmers worship Dewi Sri, the goddess of rice and fertility, and the subak irrigation system incorporates temples to honor her.

Conservation versus cash

The deities of water and life face a formidable foe. Asked if she had a message for the US president, Ni Wayan Sariati, one of Nyambu's project management team, said, "Build your hotel in America. Don't disturb us."

But tourism is by far Bali's biggest source of income, while Nyambu, the first of 22 planned ecotourism villages in Bali, hosts only around 20 tourists each month.

Ketut Mulierte, an official from the local tourism board visiting Nyambu to assess the potential of ecotourism, told DW that while he couldn't comment on behalf of his employers, Bali's priority is "economic growth, not conservation."

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