Repeated water in fuel

I have a 1989 model Ford Ranger. 4 cyl, 5 speed. Every couple of weeks it gets water in the fuel and I have to add a fuel supplement to remove it. As soon as I add it the vehicle runs fine. I have 3 other vehicles and purchase fuel at the same place for all and have no problems with them. This does not happen only when its rainy. Why does this vehicle have so many problems with water and the others don’t? What can I do to prevent this?

I would start with a new gas cap.
If the gasket on the cap is damaged, and if you live in an area of high humidity and frequent rain, it is possible that the cap could be the cause.

If that doesn’t help, then it may be necessary to drop the gas tank and examine the top of it–as well as the filler neck–for rust holes.

Yes, VDCdriver. I also recall some past problems with Ranger fuel tanks funneling water through the pump flange.

I second the fuel pump flange diagnosis. Unless it’s been changed in the past, that rubber ring is 23 years old and has probably fossilized.