Technical guidance | Fuel Right Australia
This guide supports practical fuel-quality decisions. It does not replace vessel, tank or engine manufacturer instructions, site safety procedures or qualified inspection.
Why bottom water matters
Diesel and water do not normally form one uniform phase. Free water can collect at low points, particularly in storage tanks with poor drainage or repeated water ingress. Water can support microbial activity at fuel-water interfaces, contribute to corrosion and be drawn into equipment during changes in tank level or flow. A visually clear sample from the upper fuel layer cannot rule out water at the bottom.
Identify the source before treating the symptom
Review recent deliveries, fill-cap and vent integrity, inspection records, condensation exposure, tank geometry and any alarms. Record the date and conditions of the last delivery and whether water was detected before or after it. Repeated water accumulation after removal indicates an unresolved ingress or operating issue.
Select representative sample points
Where the system permits safe access, distinguish a low-point or bottom sample from a bulk-fuel sample and a downstream sample. Label each sample with tank identification, sampling point, depth or location, date, time, recent operating conditions and collector. Do not open a tank or improvise access where confined-space, flammable-atmosphere or site controls prohibit it.
What to examine
Look for a distinct water phase, haze, sediment, corrosion particles and unusual filter deposits. Visual appearance is screening evidence, not a laboratory determination. For recurring issues, specify appropriate water, particulate and microbial analyses with a competent laboratory. A negative microbial result from one location does not establish that all tank surfaces are free of growth.
Decision matrix
| Observation | Possible interpretation | Next action |
|---|---|---|
| Free water at low point | Accumulation or ingress | Investigate source, arrange controlled removal and resample |
| Hazy bulk fuel | Suspended water or other contamination | Confirm by appropriate testing before selecting treatment |
| Slime or recurrent filter deposits | Possible microbial or mixed contamination | Sample fuel, water and deposits where practicable |
| Recurring water after removal | Ingress or operating control failure | Inspect tank interfaces and revise monitoring frequency |
Corrective action sequence
First make the system safe and identify whether fuel can remain in service. Address the ingress source. Remove accessible free water using a competent provider and site-approved methods, then assess whether cleaning, filtration, fuel replacement or other remediation is necessary. Fuel additives should not be represented as substitutes for physically removing significant free water or sediment.
Verification and recordkeeping
Document pre- and post-intervention sampling points, observations, laboratory results where used, water volumes removed, repairs, filter condition and subsequent monitoring dates. Verify the condition at relevant points rather than relying only on a clear sample immediately after intervention.
Related technical resources
For the distinctions between water phases, see free, suspended and emulsified water in diesel. For limitations of a single sample, see why a clear sample does not prove a clean tank. For equipment symptoms, see repeated diesel filter blockage diagnosis.
Practical takeaway
Water control is a system-management task: locate the source, sample the right points, remove free water safely and verify the result. No single additive or test replaces that sequence. Contact Fuel Right Australia to discuss a fuel-quality investigation or suitable treatment products.