Water is becoming increasingly important in circular economy, especially in arctic conditions. Both water and wastewater are handled in municipal treatment plants. Industry needs on-line water quality and flow monitoring. The water circulation and wastewater treatment are closely integrated with the process operation. Environmental monitoring systems rely on fairly sparse measurements. Water balances are challenging to build. Advanced data analysis and modelling are essential in taking new measurement solutions in active use. New reliable measurement solutions are needed for contaminants with very low concentration. The early detection of changes in operating conditions requires a more efficient use of on-line measurements. Uncertainty assessment, fouling detection and calibration procedures require modelling. Mechanistic, data-driven and intelligent modelling or hybrid combinations of several kinds of models are needed for simulation, monitoring, decision making, control and diagnostics. Simulation is used in evaluating the potential of new solutions in control and optimisation. For slow processes, the detection of operating conditions is enhanced with advanced trend analysis. Modelling and simulation provide efficient tools for integrating all these solutions in the control and optimisation of the monitoring and treatment processes. Strong seasonal and daily variations introduce additional requirements in arctic conditions.