An ozone generating apparatus includes a base container for holding water, and a head assembly connected to the upper edge of the base container, the head assembly containing a plurality of ozone generating cells each having a dielectric tube and an electrode assembly coaxially disposed within the associated dielectric tube. The dielectric tubes and electrode assemblies are disposed and connected such that the tube and/or electrode assembly of each ozone generating cell can be accessed independently of all other ozone generating cells, and such that the possibility of cascade failure of all remaining ozone generating cells upon failure of a single cell is substantially eliminated. The base container is provided with a process back flood prevention structure to protect the ozone generating cells.