As usual, I agree with OK4450. In my experience, a bad mechanic will frequently fall back on the old “water in the gas” excuse if he doesn’t really know what the problem is. And, all too often, friends and co-workers will automatically list that as one source of a car problem–no matter how irrelevant it may be. (The other automatic response, no matter what the problem may be is, “you need a new battery”)
Water in the gas can be a major problem–when it really exists. However, it is less likely than those well-meaning friends would have you believe.