Syria' population in percentage with the other countries that the Tigris an
This graph shows the Total Renewable VS the Total Water Withdrawal. The green is the total renewable and the blue is the total withdrawal. Syria uses more water than it gives back to the rivers. Eventually, these rivers will dry out and there will be no more water.
Water is used mostly for agriculture in this region of the world. Neither of the other options for water use come even close to the use of water for agriculture. Syria is a smaller country, so it makes sense that it doesn't use as much water as the other countries.