If there's one issue that defines marine diesel ownership, it's water in the fuel. Boats sit for long stretches, tanks breathe humid air, and condensation builds up — and at common-rail injector tolerances, water is corrosive and destructive. The good news: it's one of the most preventable causes of injector and pump failure.

How water gets in

• Condensation in partially full tanks as temperatures swing.
• Humid air drawn in through tank vents.
• Contaminated fuel from low-turnover or dockside sources.
• Long storage without treatment, which also invites microbial growth ("diesel bug").

Warning signs

• Hard starting, rough running, or surging after the boat has sat.
• White smoke or steam from incomplete combustion.
• Water or a cloudy layer visible in the fuel filter bowl.
• Corrosion or pitting found on a removed injector or pump component.

How to protect your fuel system

1. Run a quality fuel/water separator and drain the bowl regularly — this is your first line of defense.
2. Keep tanks topped off when laying up to reduce the air space where condensation forms.
3. Use the correct micron filtration for your engine and change on schedule.
4. Treat fuel during storage and turn fuel over rather than letting it sit indefinitely.
5. Inspect filters for water and growth at the start of every season.

If you've already found water

Don't keep running it — water reaches the injectors quickly. Address the source, replace filters, and have the injectors checked if you've noticed rough running. As an authorized Bosch diesel dealer, we can help you match the right filtration and fuel-system parts for your marine engine.

Before you order: verify the correct filtration and injection parts for your exact engine model.

See fuel contamination kits, fuel and supply components, and our fuel injector catalog, or contact us with your engine details.