How much water do I need to steam?

The amount of liquid you need to steam will vary depending on how long the food takes to steam and if you are steaming something that absorbs the liquid while it cooks, like rice, or gives off liquid as it cooks, like vegetables, or doesn't do either, like reheating food in a container. I have found that starting off with 2 cups of water works for most everything and that amount of liquid will last a good 20-25 minutes under steam. 

Keep in mind, the more liquid you add, the longer it will take to heat up and start the countdown. Your food is cooking while the water is heating, although at lower temperatures, it can still lead to overcooked food if you add too much liquid and don't factor in the time it takes to build the steam. 

If you are cooking foods that absorb liquid, like rice then make sure you have enough liquid to build the steam and be absorbed by the food. I have found that using 2 cups water to 1 cup white rice works perfectly for steaming rice (I set the time to 7 minutes). 

I suggest using 2 cups of water as a general rule.