At the begging of the empire, people used aqueducts for their water systems. In ancient times, Iran had lot of hills and slops. The geologists were called marganies find the spot of the underground water with a stone. People used those ground to build aqueducts. First they chose a spot to dig, then they made a small horizontal tonal underneath the surface. Then they built some vertical shafts on them. Then the water would pass through the canal and reached the surface. The average of the distance of the aqueduct was usually between 20 to 40 Km. In ancient times, this was one of the most advanced water system. Iranians were so smart and they discovered  invented and built lots of epic and incredible things, such as the water system