There are two containers for water on each side of the unit. Lift them up - by grabbing the handle - one side at a time since it holds a large qty of water. - Unscrew the bottom - and fill with water - I believe you need to use water that does not have calcium otherwise you will see a build up outside ...http://www.homedics.com//media/documents/homedics/instructionbooks/UHE-WM65_IB.pdf