"It was the number one issue that needed to be solved," says Zhang Anmeng, secretary-general of the China Ancient Village Conservation and Development Committee.

"It was also a matter of respect to tourists, especially when you are charging entrance fees."

Zhang, who has visited more than 100 ancient villages across China, says Hougou village is not alone in facing the toilet problem as these historical sites open up to tourists. But it is unique in one sense - the fact that Hougou is on the arid loess plateau means flush toilets are not an option.

Many of the cave houses were built into the hills and the construction of a sewage system is not possible without major difficulties.

"A key question was how to dispose of the waste. It would pollute the rivers as there is no sewage treatment plant nearby," Hou says.

In the past, toilets in Hougou households were simple pits that used a large container in the ground to collect human excrement. Some were open-air outhouses that only allowed privacy if the user was squatting down.

Convincing villagers to abandon time-honored habits was also not easy and the village committee had to hold several meetings to convince the residents.

In 2009, the first solution to the toilet problem in the village was brought in by Beijing-based non-government organization Clean Water, which provided funding and technical aid at the request of the China Ancient Village Conservation and Development Committee and the tourism authority of Jinzhong city.

As an alternative to flush toilets, Clean Water proposed a composting toilet system, which separates liquid from solid waste with two buckets, using plant ash to absorb the liquid and reduce the odor of the excrement.