TESTWELL is a leading designer and manufacturer of groundwater monitoring instrumentation. We have built our business and our reputation by developing rugged, dependable, accurate instruments that deliver precision and quality at a fair price, and supported by the best service in the industry. We are located in Georgetown, Ontario, Canada. Since 1990, Testwell Instruments Inc has grown to reach around the globe. We use state of the art design and the most up-to-date manufacturing technologies. We combine them with high-tech materials to ensure Testwell products provide years of dependable service. Oil/Water Interface Meters. Water Level Meters.