The present state of the saprobity system ofKolkwitz &Marsson as well as its modifications and expansions were discussed. Many critical notes were summarized and partly discussed, too. Although this system is only an empirical one and shows many insufficiencies, it is considered right. The main directions for future development, corrections and improvements are outlined and formulated in 10 items: 1. to unite all modifications into one system, 2. to recognize always the whole community and to study it quantitatively, 3. to recognize the saprobiological valency of individual water organisms statistically, 4. to make experiments in the laboratory to learn the individual factors affecting the organisms, 5. to establish a system of toxicity, 6. to establish a system of radioactivity, 7. to evaluate other non-saprobic and non-toxic effects, 8. to endeavour after the unity of all systems of the water quality in limnology, 9. to put the aspect of biological productivity into saprobiology, 10. to advance the methods of prognosis and control of water quality. The present state of these aspects of water quality is shown in tab. I–III and fig. 1.