Surface water in European countries is monitored by permanent monitoring stations by public agencies in accordance with the Water Framework Directive (2000/60/EC) and national water legislation. In addition, water companies also monitor surface or ground water near the intake of the drinking water treatment plant, but also drinking and waste water. Part of the monitoring is performed by sensors; however, these are for basic physico-chemical parameters only, such as flow rate, turbidity, pH, temperature, conductivity and pressure. Apart from these parameters and as a function of specific requirements of each site, other parameters such as chlorine, fluoride, nitrate, particle count or total organic carbon can be also monitored online. During recent years, the increase in concerns that possible deliberate or accidental contaminations might reach the final consumer, has contributed to early warning systems becoming a good alternative for water managers. An early warning system is an integrated system for online monitoring, collecting data, analysing, interpreting, and communicating monitored data, which can then be used to make decisions early enough to protect public health and the environment, and to minimise unnecessary concern and inconvenience to the public. To this end, new sensors are being placed into the market by small to medium-sized enterprises especially. Their main target is the detection of chemical and microbiological compounds, measuring single or a combination of parameters at the same time. In addition, due to the large amount of data collected, an easy to use and robust software is necessary to treat all data generated and provide clear information to the end-user. The main drawbacks at the moment to effectively implement sensors are that, on one hand, there is a lack of standards for contamination testing in drinking water both in the EU and in USA and, on the other hand, there are poor links between available sensor technologies and water quality regulations.
