I was taken back a bit when I read in the service manual about the requirements for the degassed water for testing with the wattmeter. I have not had to test the water before to find the oxygen level of the water before reading this manual... I see two methods to do so: Buy a meter to quantify or a chemical test kit like is used to check ponds and lakes for testing vitality (more oxygen=better habitat for fish and stuff). Does anyone have a preference of these choices? I am leaning toward the meter since the chemical process has some nasty chemicals such as pure hydrocloric acid.... Talk about an MSDS nightmare in my hospital setting (sigh). Currently I use an autoclave and simply "can" water in mason jars.. (I know sounds like ma and pa kettle.. Added on after reading responses: As the others have stated this is not for just "tap water", but must be free of minerals and stuff that can deposit on equipment. This process removes the gases from the water only.. I did not state that the first time and needed to be clarified..