A water tank empties at a rate of litres per minute.
There were litres of water in the tank.
How many litres of water are there left in the tank after 2 hours?
Since the tank empties at a rate of x litres per minute, it empties x * 60 = 60x litres per hour.
After 2 hours, the tank will have emptied 2 * 60x = 120x litres.
Therefore, there will be 120x - 120x = 0 litres of water left in the tank after 2 hours. Answer: \boxed{0}.