The permittivity of water is considerably larger than that of air. As the amount of water in PVC water pipes increases, the air will be replaced by water. This means that the electromagnetic environment properties inside the pipe will change. In this study, we proposed a microwave clamp probe designed with a 3D printer that can detect the percentage of water in 50 mm diameter PVC water pipes. The clamp probe allows measurement of return loss from a single port for determining the fill rate of water without any physical intervention from outside the pipe. The clamp, which is structurally similar to a loop antenna, operates at a frequency of 2.45 GHz. As a result of simulations and experimental measurements for different fill percentages of the pipe, the input impedance of the clamp was calculated. Then, an impedance-fill rate graph was created, showing the amount of water in the pipe section according to the impedance values obtained. The impedance seen from the clamp input indicated a linear increase between 40-100 Omega, according to the 0%, 20%, 50%, 80% and 100% of the water in the pipe. The clamp has a compact structure that can be used as a plug-and-play anywhere on the horizontal.