To enrich the water with oxygen  the water is sprinkled through a reactor or pressure barrel which  is partly  filled with pure oxygen. This occurs under a pressure of 0.5 - 4 bars. 

Because the reactor is closed almost no oxygen is lost. All models are delivered with  junctions, gauge-glass, pressure gauge and safety valve.

In the scheme below is indicated how an oxygen reactor  can work.

SCHEME: WORKING OXYGEN REACTOR 

The probe constantly measures  the oxygen content. When the percentage of oxygen is under a certain level that has been adjusted manually,  a measuring unit will bring more oxygen  into the reactor. When the grade of oxygen descends  to an unacceptable level, oxygen is dosed directly through a tube.  

 TYPES OF OXYGEN REACTORS