How much water do I use for 2 cups of rice in a rice cooker?
How much water do I need for 2 glass of rice in the cooker?
It is depend on how you are cooking your rice.

If you are cooking in pan then ratio is 1:2.5 means 1 glass rice then water shoud be 2–1/2 glass.
If you are cooking in pressure cooker then ratio is 1:1–1/2 means for 1 glass rice then water should be 1–1/2 glass.