I also use the blue torpedo type water filter but in conjunction with the stock water filter system. I am thinking of changing the stock water filter for a GE smart water systems filter...Cartridges are much cheaper and can be bought almost anywhere (Home Depot, Walmart and Lowes). Also, it has the added bonus of having a 3 position lever... Bypass, Off and through the filter modes. I put one on my prvious TT and it was a lot easier to winterize because the clear housing didn't have to be filled with "pink" fluid.
2008 Dodge Ram 4X4 Quad cab LB 2500 Cummins 6.7L TD / 2013 Columbus 320rs. Camped 50 days in 2015. RIP Angel the camping Cat, we will miss you.