Traditionally chemicals in the aquatic environment (e.g. nitrate, phosphate) are measured by manual collection and laboratory analysis of discrete water samples. Microfluidic sensors offer an attractive alternative: by taking and analysing samples autonomously in the environment, they remove the need for manual sampling and allow real-time monitoring of water composition and quality. The current state-of-the-art sensors are not widespread due to a range of issues, most notably complicated fluidic control and their inefficient use of chemical reagent. This increases the size of the sensor and its power consumption, limits the frequency that measurements can be taken and duration the sensor can be deployed each time. Droplet microfluidics (in which nanolitre water samples are taken and subsequently operated on as droplets within an immiscible oil) is a novel microfluidic method that, in addition to other advantages, crucially offers higher analytical throughput and much more efficient use of consumables (reagent consumption being orders of magnitude lower). We have previously developed and demonstrated the first-ever droplet microfluidic sensor prototype for measuring nitrate and nitrite that uses drastically lower reagent consumption relative to the current state of the art. In this project we will mature the technology and demonstrate it in real-world operation in partnership with end users, including a UK public body and Chinese water company. These demonstrations will help us to refine the sensor, demonstrate its effectiveness, and ready it for commercial exploitation.