What Causes Water Contamination in Fuel Tanks?

Water contamination is one of the most common threats to stored fuel quality. Water in a fuel tank can lead to microbial growth, corrosion and blocked filters, while also increasing the risk of damage to pumps and other fuel system components.

For businesses relying on stored diesel for generators, vehicles or critical equipment, these issues can contribute to reduced reliability and costly downtime.

The difficulty is that water can accumulate inside a fuel tank without obvious signs, making regular fuel tank inspection and fuel monitoring essential.

Why Is Water in a Fuel Tank a Problem?

Because water is denser than diesel, free water typically settles at the bottom of the tank. Over time, this can create conditions that contribute to:

• Microbial growth, also known as diesel bug
• Internal tank corrosion
• Sludge and sediment
• Blocked fuel filters
• Fuel degradation
• Damage to fuel-system components
• Equipment downtime

Water also provides an environment in which bacteria, yeasts and fungi can develop, particularly around the fuel-water interface.

What Causes Water Contamination in Fuel Tanks?

Condensation

Temperature changes can cause moisture in the air inside a fuel tank to condense on internal surfaces. The resulting water droplets eventually settle at the bottom of the tank.

Partially filled tanks may be more prone to condensation because the increased headspace contains more air in which moisture can be present. Over time, repeated condensation can result in significant water accumulation.

Damaged Seals, Covers or Vents

Worn seals, damaged inspection covers, defective fill points and poorly maintained vents can provide routes for rainwater or surface water to enter a fuel tank.

At BMS Group, we provide routine inspections that can help identify deterioration before it results in contamination.

Contaminated Fuel Deliveries

Although less common, water can occasionally be introduced during a fuel delivery if contamination exists elsewhere within the supply chain, storage facilities or delivery equipment.

Once introduced, the water can settle at the bottom of the tank and remain unnoticed without appropriate fuel sampling or water checks.

Poor Tank Maintenance

Small quantities of water may accumulate for months or even years without creating an obvious problem.

Without routine fuel sampling, water checks and tank inspections, contamination can continue to develop until it begins affecting fuel quality or equipment performance.

How Does Water Cause Diesel Bug?

Water contamination can create the conditions required for microbial growth, commonly referred to as diesel bug.

Bacteria, yeasts and fungi can develop around the interface between diesel and accumulated water. As these microorganisms grow, they can produce sludge and deposits that contaminate the fuel system.

Common consequences include blocked filters, internal corrosion, degraded fuel and reduced equipment reliability.

Repeated filter blockages can therefore indicate a wider contamination problem within the fuel storage tank rather than simply a faulty filter.

Signs of Water Contamination

Water contamination is not always immediately visible, but warning signs can include:

• Water or separation visible in fuel samples
• Sludge or sediment
• Recurring blocked filters
• Internal tank corrosion
• Changes in fuel appearance
• Unexplained equipment performance issues

It’s important to identify these problems before they become more serious.

How Can Water Contamination Be Prevented?

A proactive fuel tank maintenance programme can significantly reduce the risk of water and microbial contamination.

Key preventative measures include:

• Regular fuel sampling
• Routine water checks
• Periodic tank inspections
• Tank cleaning when required
• Maintaining vents, seals and covers
• Monitoring fuel condition over time

• The right maintenance schedule will depend on several factors, including tank type, operating environment, fuel turnover and how critical the equipment it supplies is.

  BMS Group’s fuel management specialists can provide expert advice, regular fuel sampling and tank inspections to help identify potential issues early, minimise downtime and avoid costly repairs. To speak with a specialist or arrange your next tank inspection, call us on 0345 230 7887 or email sales@bms-ltd.com.

Protect Your Fuel and Equipment

Preventative maintenance is generally far more cost-effective than dealing with contaminated fuel, damaged equipment or unexpected downtime.

If you are unsure about the condition of your fuel or storage system, BMS Group can help assess, inspect and maintain your fuel storage assets, identifying potential problems before they develop into more costly failures.

Regular fuel sampling, tank inspections and preventative maintenance can help protect fuel quality, equipment reliability and the long-term condition of your storage system.

To arrange your next inspecaion or speak to BMS Group’s fuel management specialist, call us on 0345 230 7887 or email sales@bms-ltd.com.