Condensation is naturally formed when certain foods like vegetables, fruits, leafy green and cheese, etc. are stored in the containers.

Food sealed in the contained no longer has air flowing in and around it.  Normally we don;t see the moisture come off food, but because it is sealed in the container, any moisture or humidity the food naturally produces is captured on the inside of the container.  This DOES NOT mean your container is leaking in air or that it is broken, it is something that happens naturally.

To combat this issue, place a few pieces of paper towel in the bottom of the container and an extra piece on top of the foodstuff to absorb any extra condensation.  This may not get rid of the condensation, but it will help.

See section entitled "Foods Requiring Extra Care" for some more specific ideas on storing certain foods.