Why is there water in diesel fuel? Is it a condensation problem? Or rain that finds its way into the holding tanks at stations? Would using diesel additives such as Diesel Kleen really help? 2005 B5 and 2009 Q7 TDI.
PowerService Diesel Kleen is good stuff but it doesn't do anything for water. Use the PowerService Diesel Fuel Supplement (white bottle) stuff instead.
Water in Diesel fuel? YES! Always.
More so in winter compared to summer. Even with the driest diesel fuel available, there is always a small amount of dissolved water present. The dissolved water normally isn't a concern. It's slugs of free water that have dropped out of suspension that you need to worry about.
It only takes a single tank of water-contaminated fuel to do a lot of damage to an expensive injection system.
Diesel fuel is hygroscopic, meaning that it holds onto water and soaks it up like a sponge. It willl soak up water over time. It's worth it to regularly use an additive that increases lubricity and does something for water.
To make sure you're getting only the freshest and driest fuel in your area, stick to fueling up only at truck stops and high volume gas stations along major routes. Go where the big rigs go. Basically buy your fuel where everybody else does in your area. This is particularly important during the winter months. The fuel will always be the freshest and driest at these stations because it's constantly being replaced often. Avoid fueling up at stations that rarely get any diesel business, no matter how tempting the slightly lower price per gallon may be. Over time and through experience you'll learn which of your favorite high turnover stations have the best quality fuel and then stick to fueling up only at those stations.
I've been following the simple rule above since day one with my 02 golf TDI. After "only" 354k miles, it is still on it's original
injector pump with no issues.