We have developed a new online water cut meter using low field Nuclear Magnetic Resonance (NMR) technology. This instrument is designed for use with heavy oil systems where conventional instruments experience difficulties. We describe the process of developing and implementing this new technology. Data from successful field tests near Cold Lake, Alberta, Canada, shows that the instrument is capable of making water cut measurements over a wide range of fluid types and temperatures. The instrument is capable of functioning accurately where a wide range of emulsions and/or foams exist and where he salinity of the water phase can go through significant variations. The current application is for water cut measurements on wellsite. The instrument can be applied in any system where heavy oil/bitumen/water/gas/solid systems may be encountered. It can be used for water cut volume or mass fraction measurements. The instruments is equally capable of performing wellsite monitoring for regulatory/reconciliation purposes, for characterizing produced fluids in separation, pipelining, and upgrading processes for process control, and for quality testing.