The purpose of the invention is to simply know the concentration of a water treatment agent on the spot where a heat device is installed. A method for determining chelating agent includes a step of collecting sample water, a step of respectively adding a first chemical solution containing a metal indicator and a second chemical solution containing a pH controller to the collected sample water, a step of dripping a third chemical solution, which contains a metal salt for discoloring the metal indicator, on the sample water to which the first chemical solution and the second chemical solution are added and counting a dripping number until the sample water is discolored and a step of specifying the concentration of the chelating agent in the sample water on the basis of the dripping number ofthe third chemical solution. The measuring kit includes a first container in which the first chemical solution containing the metal indicator is housed, a second container in which the second chemical solution containing the pH controller is housed and a third container in which the third solution containing the metal salt for discoloring the metal indicator.