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Water in DEF Tank? Understand the Causes, Effects and Solutions

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understanding water in DEF tank

Water in diesel exhaust fluid (DEF) tanks is bad news — whether the tanks store DEF in bulk or in smaller amounts within diesel engine vehicles.

Because of the harmful effects, you might consider water in DEF a type of fuel contamination despite DEF’s not meeting the definition of a fuel. Water in DEF tanks doesn’t get as much attention as diesel bugs, but the effects include lost product and vehicles that won’t run. It makes good business sense to keep water out of DEF and diesel storage tanks, alike.

Below are the causes, effects and solutions for water in DEF tanks so you can keep your equipment and vehicles operating at peak performance.

Can You Put Water in DEF Tank?

No, never put water in a DEF tank. Confusion and bad internet advice about water in DEF tanks likely exists because diesel exhaust fluid is mostly water. The composition leads people to assume that topping off their DEF tanks with a little more water won’t hurt anything. But this is wrong. When water makes its way into DEF storage tanks or DEF tanks on vehicles, things can go awry quickly.

DEF, also called AdBlue, is clear like waterDiesel exhaust fluid is a clear liquid like water, but DEF (also called AdBlue) doesn’t contain regular tap water, which contains minerals and ions. DEF is 32.5% synthetic vehicle-grade urea (ammonia) and 67.5% deionized water.

For a diesel vehicle’s selective catalytic reduction (SCR) system to bring about catalytic conversion and reduce nitrogen oxide (NOX) emissions, the proper concentration of deionized water must be used.

Causes: How Water Gets Into DEF Tanks

Water can make its way into DEF storage tanks two ways:

  1. When DEF is stored in bulk.
  2. When DEF is stored in vehicle tanks.

Water in DEF Bulk Storage Tanks

Water in DEF bulk storage tanks and DEF transfer tanks can occur when owners overlook regularly scheduled inspections, maintenance and repairs and when they use the same tanks for different products.

Without performing regularly scheduled tank inspections, owners risk going about business as usual and missing easily resolvable problems that otherwise can turn into disasters. One problem owners tend to overlook without consistent tank inspections is water condensation that might have formed within tanks’ air voids during fluctuating temperatures. Other problems that inspections flag include faulty fittings and seals and simple human errors, such as leaving a lid off a tank.

Water in DEF Vehicle Tanks

Water contamination of vehicle DEF storage tanks at the vehicle is preventable. The simplest way? Never put any kind of water in your vehicle’s DEF tank. As with any fuel cap on a vehicle, ensure the DEF cap is sealed tight after every fill. This will keep rain and water from car washes out of the DEF tank.

Effects: Symptoms of Bad DEF Fluid

Symptoms of bad DEF fluid include a DEF color of anything besides clear, including cloudiness. In addition, bad DEF fluid contaminated with water can lead to equipment failure and can void manufacturer warranties. Other effects and symptoms to watch for include:

  • Check engine light. Something’s not right. Don’t ignore this.
  • Crystallization: Evidence shows that when people have topped off their vehicles’ DEF tanks with hard water, deposits can form in the SCR systems’ exhaust or injector nozzles.
  • Diluted DEF: Water in excess of 67.5% reduces the effectiveness of DEF NOX neutralization.
  • Increased DEF consumption.
  • Vehicle slows or stops.

Solutions

Water in DEF Bulk Storage Tanks

DEF bulk storage tank inspections can prevent water in DEF

 

  • Inspect DEF bulk storage tanks as part of your regularly scheduled maintenance routine.
  • Ensure DEF tanks remain watertight so rain and snowmelt cannot enter the tanks.
  • If anything on a tank does not pass inspection, repair or replace the tank.
  • Verify DEF quality when DEF is delivered or when it’s in bulk storage. To do this, request the Certificate of Analysis from your DEF supplier. As an alternative, you may submit a sample for testing according to ISO 22241-1.
  • Test DEF for minerals such as calcium and deposit composition using ICP Spectrometry or XRF Spectrometry.
  • You can use a handheld DEF refractometer to measure fluid concentration specifications. An acceptable measurement of urea concentration reads between 32.5% and 37%.

How to Clean DEF Tank

If you suspect anything besides pure DEF has been inside your DEF tank:

  • Drain the tank and flush it with deionized water or new diesel exhaust fluid.
  • When your DEF tank is empty, rinse it with warm water.
  • Clean, dry and reassemble the tank.
  • Fill the tank with fresh diesel exhaust fluid.

Water in DEF Vehicle Tanks

  • Check for crystallization on exhaust piping and DEF injectors.
  • You can use some of the sampling and testing procedures for bulk storage tanks.

More Resources

Need Help? Ask the Experts

For help in choosing the right DEF storage tank or DEF transfer tank, it makes sense to ask the experts. Unity Fuel Solutions is North America’s leader in double walled storage tanks. For advice on the tank and system that’s right for you, call the Unity team at 800-234-1689.

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