JERUSALEM — Twenty feet under the ancient City of David and modern-day Jerusalem, a murky stream of water runs through the city’s bedrock like a vein to the heart of the Holy Land.

The Gihon spring has flowed intermittently through this rock for thousands of years. For most of that time, it was Jerusalem’s only water source, and its supply was unpredictable. True to its name, Hebrew for “gushing,” the spring could lie dry and empty for days at a time before suddenly bursting forth with water. Today, five years into a debilitating regional drought, Israel’s water supply is just as tenuous.

“The fertile crescent used to be fertile,” says Pinhas Alpert, a professor of atmospheric sciences at Tel Aviv University. “It’s not anymore. We’re undergoing a dramatic decrease in rainfall.”

According to Israel Meteorological Service, Jerusalem saw only 67 percent of its usual rainfall this year, the latest statistic in a multi year-long downward trend. And as global temperatures continue to rise in years to come, the region is expected to grow even drier.

“The people living in this land are much more dependent on God to pray for the rain to come,” says Rabbi Yonatan Neril, the founder of the Interfaith Center for Sustainable Development, a nonprofit which strives to mobilize believers from different faith traditions to promote environmental causes. Its efforts represent part of a growing interfaith community calling for water conservation and sustainability in Israel.

“Israel is different from Egypt, which has the Nile, and from Iraq and Syria and Turkey, which have the Euphrates and Tigris Rivers,” he says. “So the water situation in Israel is much more vulnerable. It depends on the rain, and I think that’s by divine design.”

Whether God or nature designed it all this way, water has been central to Jerusalem’s survival for as long as the city has existed. And for a window into the relationship between water, the Israelites and God, you need look no further than the Gihon spring.

“When you see archaeological artifacts – clay pots – they’re dead. But the spring is living,” says Asher Arbit, a tour guide and archaeologist with the City of David tour company. “And it’s why Jerusalem exists here. Because of this water.”

Arbit’s shoes squelch with sacred water as he wades through the 533 meter-long tunnel where the Gihon spring flows. Equipped with a headlamp and an extensive knowledge of Jerusalem’s ancient history, he guides visitors through knee-deep water, bringing biblical tales to life as they wind their way through the dark and narrow tunnel.

Asher Arbit, a tour guide with City of David tour company, points to the spot on Jerusalem’s hilly landscape where the mouth of the Gihon spring was located in ancient times. (Godland News / Sarah Wyman)

For thousands of years, the lives of Jerusalem’s inhabitants have been intertwined with the gently-trickling stream. Arbit traces the grooves in the hard rock wall with his hand as he recounts how, in 1010 BCE, King David’s troops invaded the subterranean water system to conquer Jerusalem. Three hundred years later, King Hezekiah engineered a tunnel to divert the supply inside the city’s walls, guaranteeing Jerusalem’s inhabitants safe and reliable access to clean water. And for thousands of years, the faithful have drawn water from the Gihon spring during the Jewish festival of Sukkot. It is used during the water libation, which celebrates the fertility of the land and the Israelites’ dependence upon God for survival.

“It’s really about praying for water,” says Rabbi Neril. “And also showing gratitude and thanks for when the rains do come.”

Neril is sitting in a bright office a few miles south of the Old City that looks like it could have been lifted out of a Silicon Valley startup. Colorful furniture is arranged throughout the open workspace, and sunlight streams into the room through an expansive bank of windows.

The office is home to several sustainability-oriented groups, many of which share religious roots. Though Neril is happy to discuss the theological foundations of his work – he’s edited two books and a series of videos and podcasts about the connection between water and Jewish teaching – his activities go beyond religious study and prayer.

“We’re in the bottom of the ninth here,” he says. “It’s about survival.”

Neril’s organization, the Interfaith Center for Sustainable Development, is acting with some urgency in the face of this challenge. Together with Palestinian and Jordanian seminary students, Neril and his colleagues lead seminars about the connection between the Jordan River, faith and water conservation. Their aim is to unite the region’s faith leaders in their efforts to make clean water available to everyone and ensure their society’s survival in decades to come.

“My ecological concern isn’t like an appendage pasted on to my religious identity. It’s really one and the same,” says Neril.

Thousands of years have passed since the spring of Gihon first bubbled from Jerusalem’s bedrock, answering the prayers of the Israelites who lived there. Today, it continues to serve as a living reminder of how insecure survival is in this place, how uncertain it has always been and how much it depends on nature’s cooperation. As Neril and his colleagues know well, life in Israel is metered by an existential thirst. Its fate is – and has always been – intertwined with nature and the will of God.

“What happens to the waters is a religious issue.”