The Islamic Republic of Iran faces a growing water crisis. Iran's average available renewable water resources total 137 cubic kilometers (km3) per year. Iran subsidizes municipal water demand as well. Like farmers, domestic customers pay considerably less than the actual cost of provision. Food and energy subsidies distort the amount and geographical distribution of Iran's water demands. Continuing global climate change threatens to further strain Iran's water security, diminishing the quantity, degrading the quality, and disrupting the seasonal timing and geographical distribution of available water supplies. Iran's water challenges also hold international repercussions. Iran shares 10 major river systems with surrounding countries. Absent robust collective arrangements, rows over common water supplies are firing regional tensions. Iran and the US face important infrastructure challenges, such as refurbishing aging municipal water systems, as well as opportunities for innovation, such as desalination technologies and wastewater treatment and reuse.