ANSWER: Hi Jim OK, I am sure that what I am about to tell you will freak out some RVers. The color in your water is in all likelihood being caused by Algae and believe it or not it is very common for RV Freshwater holding tanks to have a coating of algae in them and in most cases the RVer will not even know it.
The fact that your water is green is a clear sign that the Algae is out of control in your freshwater tank.
My suggestion is that you sanitize your RV's fresh water holding tank. As they say a picture is worth a 1000 words. In this case a video is worth a lot more. Take a look at the video below from RVing Expert Mark Polk on what you need to do to sanitize your RV's Fresh Water System.
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