New FORD Groupie!

[Wild Mann]

Hello everyone! I'm glad I found this site. I have two, three really, Ford trucks I am fiddling with when I can and I've had a lot of trouble finding information about my troubles when I need it. I seem to run into the craziest things on these rigs.
I have an E-150 which will be my daily driver, when I finish it, and two F-250's, one wreck and one blown engine, that I am going to combine into one functional vehicle. More on that later.
I'm asking for my E-150 which has now given me the ultimate fit, so it seems. I had problems with it stumbling and dying in idle unless I kept some pressure on the accelerator pedal . I finally traced that problem to the idle air mixing valve and replaced it. Unfortunately. I had to let it sit for too long before I could drive it again after the repair. When I finally got it on the road, the first thing it does is die about one mile from my house. Took it back home and worked on it on and off for a while. Never could get it to run for more than a few seconds at any time. I have twin tanks on it and neither tank made a difference. I had made sure to put some fresh gas into the tanks and idle it from both tanks for a period of time to be sure fuel was flowing. This was when it died after a mile on the road.
I fiddled with it for awhile and decided the primary fuel pumps had died or the filter screens were varnished over causing the pump to die.
Today I dropped the rear tank and found it half-full of water. No wonder it wouldn't run and this is probably why the pump quit. Anyway, the hoses are sound, the cap is still tight on the fuel fill inlet and the tank is solid. Could anyone give me some info about how this water could have gotten into the tank?
I only used gas from "name" suppliers and I don't think I could have gotten that much water from the few stations I have visited since the last time I drove it. I believe it had to have gotten in from some other outside source. Any ideas are appreciated. Thanks!!