As per the 1960 Indus Water Treaty governing six common rivers, India has full rights over the Ravi, Beas and Sutlej rivers while Pakistan has full rights over the Jhelum, Chenab and Indus.
This treaty has set up a grievances redressal mechanism. Each country has its commissioner. If there is a dispute these two commissioners meet to sort out the problem.
If they cannot reach an agreement, then they go to the foreign secretary level and failing that, the government. If the problem is not solved there as well, then they go to a neutral expert.
That neutral expert panel is decided by these two countries. In the past neutral experts were from Europe and the US. Now even if they fail, then the issue goes to the International Court of Justice.