I had a fresh water leak last year, that I have spent a lot of time, trying to find the source. It leaked above my diesel fuel tank and I couldn't get above it, to see where the water was coming from. I thought I was going to have to drop the fuel tank, to be able to find the problem. However, this week, I made a greater effort to see above the tank, by opening the driver's side slide. When I crawled under the coach, I found an inspection panel above the chassis frame. I thought this could be the way, so I removed the screws and took the panel down. The second picture, shows just what I wanted....the water tank! Actually, there are 2 white tanks, inline and above the fuel tank. They are connected by a white hose, about 1 & 1/2" in diameter and fastened to the tank with hose clamps. Walla! I said "there's my leak"! One of the hose clamps was loose and dripping water!
So, I tightened the clamp, as tight as I could, replaced the panel and "NO MORE LEAKS"! Now, the square bar, that runs along side the inspection plate does not have to be removed, but it is a lot easier to remove/replace the panel if you remove it. Except for rusted bolts, it was easy to remove.
For the OP that initiated this post, keep looking and hopefully, you can find the inspection panel.