An autonomous microfluidic analyser for phosphate in wastewater and environmental waters has been developed and validated in laboratory and field trials. The analyser is based on the molybdenum yellow method for phosphate detection in which a phosphate-containing sample is mixed with a reagent containing ammonium molybdate and ammonium metavanadate in an acidic medium. The yellow-coloured compound which is formed absorbs strongly below 400nm and its absorbance is proportional to the concentration of phosphate in the original sample. The analyser utilizes a microfluidic manifold where mixing, reaction and detection take place. Optical detection is performed using a LED (light emitting diode) light source and a photodiode detector, while wireless communications allow near real-time access to the collected data. The analyser also combines pumping system, power supply, reagent and waste storage, and wireless communications into a compact and portable device. The system has been successfully applied to analysis of treated wastewater at a treatment plant in Co. Kildare, Ireland. In parallel with this work, detection schemes for other targets (ammonia, nitrate/nitrite, pH) have been assessed, with the goal of developing a low cost, field deployable multi-analyte detection system. Utilising colorimetric chemistry and LED-based detection systems allows a modular approach which facilitates integration of the new detection schemes with the hardware platform provided by the phosphate sensor.