A selective and sensitive method is described for the microdetermination of phosphate in water and wastewater employing a new reagent system. The method is based on the reaction between ammonium molybdate, PVA (stabilizer) and malachite green (lambdamax 600nm). Beer's law is obeyed up to 10ppm. The use of PVA as a substitute for Tween 20 makes more soluble the malachite green-phosphomolybdic acid complex; it becomes more sensitive and less of reagents are needed to obtain the same sensitivity as when Tween 20 is used as a stabilizer. It offers advantages like reliability, non-interference by silicates and reproducible in addition to its simplicity, instant colour development and allows economy in reagents such as ammonium molybdate and malachite green. It's cost is less than half of the Tween 20 method. This method is more suited for the measurements for the range of 0.01 to 10 mg p/L.