The qanat or karez irrigation system brought water from the highlands to the lowlands through a series of underground canals and reservoirs. By keeping the water underground, less was lost to evaporation and this made arid regions bloom. It was, however, labour-intensive to maintain, and without a population to maintain it the karez system broke down and arable areas returned to scrub or desert. The system had been widely used since the ancient period, and some areas of Central Asia, Iran and Afghanistan still use it today. Access points followed the underground portion and permitted repairs to the underground channels. Additionally, the water cooled these spots, providing relief to workers during the summer.