A prototype instrument was developed for automatically monitoring total phosphorus in water. The analytical principle employed was flame emission photometry. Phosphorus compounds burned in a hydrogen flame emit at about 525 millimicrons. Conditions were established for the sensitive measurement of phosphorus in water. Operating parameters investigated included fuel and air flow rates burner configuration, operating temperature, method of sample aerosolization, etc. Using an ultrasonic nebulizer to aerosolize samples of triethylphosphate in water, it was possible to detect phosphorus at a concentration of less than 2 parts per billion. A procedure was worked out for distinguishing between organic and inorganic phosphorus with ion exchange resins. In measurements designed to determine interference by sodium and calcium, it was observed that the method is about 1000 times more sensitive towards phosphorus than towards sodium and 5000 times more sensitive towards phosphorus than towards calcium. A prototype instrument was designed, fabricated, and tested.