There is a large number of industries that rely on water or other fluids periodical quality analysis for meeting regulatory requirements or for ensuring safety and security for the population. This need has led to the development of real-time monitoring and on-line analysis instruments that have become a major trend nowadays. On-line analysis of water quality is necessary in the food and the aquaculture industries. The pharmaceutical industry has also the same need and in this case not only for water quality analysis, but also for the analysis of other fluids used for pharmaceuticals production.One of the major problems when dealing with on-line fluid analysers is sample filtration. In fact, in all aforementioned examples of application, the sample cannot be used directly for the analysis. Furthermore, for on-line analysers, sample contamination is also a problem due to the frequency of the analysis. Some technical solutions have been developed and used for overcoming this issue, including self-cleaning filters. Nevertheless, those solutions are very expensive and large in terms of dimensions, thus applicable only to specific application fields where cost and size might not be an issue. Most importantly, the lifetime of such solutions is still limited, while in many cases such filters cannot guarantee high retention rates.On-FiSy project answers the need of the on-line analysers industry for a low-cost, compact, flexible and reliable automatic liquid sample filtering device. The overall objective of the On-FiSy project is to design, develop and verify an automated multistage filtration concept to be used in various types of on-line liquid analysers. The On-FiSy prototype device is based on the use of common, low-cost filters combined with a novel, automatic filters replacement mechanism and a smart, modular design for combining multiple filtration steps in a single process. The concept will be verified through a prototype to be developed and used for laboratory tests, reaching TRL 4.The project On-FiSy (CONCEPT/0617/0004) is co-funded by the European Regional Development Fund and the Research Promotion Foundation of Cyprus.