Most gas stations do NOT add water to their tanks, and that's a fact. What also is a fact, is that older stations (over 30 years old) have old tanks in the ground, which, after having been there for 30 years, have a seepage problem. That is, that when it rains and the ground gets saturated, water seeps into the tank. There are a few stations here which were shut down because the gas/water mix was well above what it should be, and the owners didn't even know it. Come to find out, they thought they had I think an 800 gallon tank in the ground, but it was actually 1500 gallons! That's how much water was filling it up (and the bottom of the pickup tube had rotted away, so it would act empty when there was a good 600 gallons of water in it). Needless to say, they either closed down or replaced the tanks to stay in business. Some also just pumped out the water and kept right on doing business, which isn't the best thing to do, but it's better than selling watered down gas. And yes, water and gas don't mix, but with the way the gas is always moving in the tank from being pumped into vehicles, and the fact that the pickup has to be near the bottom of the tank, it can pick up water if there's enough in the bottom. Also, injecting a small amount of water into your engine doesn't do any harm. In fact, it was used in WW2 in the fighter planes to increase power, as it cooled off the air (making it more dense) and reduced detonation, which allowed them to build more powerful engines. In a P-51 mustang it could increase top speed by as much as 50mph. So a small amount of water is not only unavoidable, but actually helps. You just don't want to fill the cylinder with water. Remember, the computer only injects 1 part of water/gas for every 13.5-14.5 parts of air, which is a very small ratio in comparison.