Aeration with the commercially available LIMNO aerator has now been in use for about 10 years. Over 40 aerator units have been installed and successfully operated in nine different projects. From the abundant experience gathered during this relatively long period some examples are chosen to illustrate the efforts on increased mineralization capacity of allochthonous and autochthonous organic material. The ubiquitous eutrophication problems especially degrade water quality in lakes and reservoirs. Excessively produced algal material in the hypolimnetic layer leads to serious anoxia, preventing higher life and aerobic respiration processes. Furthermore, internal recycling processes connected with the metabolic and geochemical cycles of manganese and iron enable the multiple use of recycled phosphorus. All of these processes are possible to control by aeration. On the other hand, necessary treatment for drinking water preparation, such as filtration, flocculation, and chlorination can be reduced if a sufficient oxygen balance is maintained in the hypolimnetic water body. Results are presented from two drinking water reservoirs and some lakes where drastic improvements were observed.