AdBlue is roughly one-third automotive-grade urea and two-thirds deionised water by mass — that split is deliberate and exact, not a sign of a weak or diluted product. The three numbers that actually define quality are density (1.087–1.093 kg per litre at 20°C), urea concentration (31.8–33.2% by mass) and purity — the near-total absence of metals, phosphate and other impurities. Each protects a different part of the vehicle, and understanding what they mean makes a supplier's specification sheet much easier to read.
Why AdBlue is mostly water — and why that's correct
An SCR catalyst needs ammonia to convert nitrogen oxides into nitrogen and water. Urea, heated in the hot exhaust stream, breaks down and releases that ammonia. But pure or highly concentrated urea doesn't dose, atomise or decompose in the exhaust the way a precisely diluted solution does — the roughly 32.5% concentration in ISO 22241 is the point at which the chemistry works reliably across the wide range of temperatures and engine conditions a vehicle actually operates in.
So when a specification sheet or a safety data sheet lists water content under 70% by weight, that's describing the correct product, not flagging a problem. The water isn't a filler — it's precisely how much is needed to bring pure urea to the concentration the SCR system was engineered to use.
Density: the simplest field check
Density measures how much a given volume of the fluid weighs, and for AdBlue it moves in lockstep with urea concentration — which is exactly why it's useful. ISO 22241-1 sets density at 1.087–1.093 kg per litre at 20°C. Measuring it with a hydrometer is a valid, if less common, alternative to a refractometer for checking concentration is roughly in range; our quality-checking guide covers both methods.
Density changes with temperature, so a reading needs correcting if the sample isn't close to 20°C — one reason most buyers reach for a refractometer instead, which is quicker to use in the field.
Urea concentration: the number that matters most
This is the figure the ISO 22241-1 range of 31.8–33.2% by mass describes directly, and it's what a refractometer test checks in about a minute. Too low, and the SCR system doses too little ammonia relative to what its control unit assumes, which raises NOx emissions and can trigger a fault. Too high, and the system risks wasting urea and forming deposits — concentration outside the range in either direction is a real problem, not just a technicality.
Purity: what a concentration check can't see
Density and urea concentration both describe the "how much" of the solution. Purity describes the "what else" — and it's the part you cannot check without a laboratory:
- Metals — calcium, iron, copper, zinc and others — are limited to fractions of a milligram per kilogram, because they deposit permanently on the SCR catalyst surface.
- Phosphate is limited for the same reason.
- Aldehydes indicate lower-grade urea feedstock.
- Insoluble matter blocks filters and injector nozzles.
These limits are why AdBlue must be made with deionised water rather than tap or well water, and handled only with equipment kept exclusively for AdBlue — ordinary water and residue from other fluids both introduce exactly the impurities these limits exist to exclude.
Reading a specification sheet
Put together, a genuine AdBlue specification sheet should show:
| Property | ISO 22241-1 requirement |
|---|---|
| Urea content | 31.8–33.2% by mass |
| Density at 20°C | 1,087–1,093 kg/m³ |
| Water content | The remainder — roughly two-thirds by mass |
| Metals (calcium, iron, copper, zinc, etc.) | Fractions of a mg/kg, individually limited |
| Phosphate | 0.5 mg/kg maximum |
A supplier who publishes these figures, batch by batch, is showing you the product rather than just describing it. Our own quality-checking guide has the full limit table from the standard, including alkalinity and biuret.
Common misreadings of these numbers
- "70% water" sounds diluted — it isn't. It's the correct, specified composition, not evidence of tampering.
- A density reading alone doesn't confirm purity. Water contaminated with the wrong minerals can still land near the right density; density checks concentration, not what else is in the fluid.
- A concentration in range doesn't guarantee the water was deionised correctly. That's a purity question, and it needs the manufacturer's own testing behind it — see our genuine vs counterfeit guide for how to weigh that alongside a field test.
How SiriusBlue publishes these figures
SiriusBlue blends AdBlue at its plant in Riyadh and checks every batch against the values on its current safety data sheet before release — density, pH, urea content and water content are published on our homepage rather than simply described. If you want to verify a batch yourself, our quality-checking guide walks through the refractometer test step by step.
Quick answers
Is it normal for AdBlue to be mostly water?
Yes. AdBlue is roughly two-thirds deionised water and one-third urea by design — that's the composition ISO 22241 specifies, not a sign of dilution.
What's the difference between density and concentration?
They describe the same underlying property from different angles: density is a physical measurement (weight per litre), and urea concentration is the chemical measurement (percentage by mass) it correlates with. Both should fall within the ISO 22241-1 range.
Can AdBlue be too concentrated, not just too diluted?
Yes. Concentration above 33.2% is also outside the ISO 22241-1 range and risks wasting urea and forming deposits, even though it isn't the more common problem.
Does a correct density reading mean the fluid has no contamination?
No. Density and concentration checks confirm the "how much"; purity — metals, phosphate and other impurities — needs laboratory testing to confirm.
Key points
- AdBlue is roughly one-third urea and two-thirds deionised water by design — that split is correct, not diluted.
- Density (1.087–1.093 kg/L at 20°C) and urea concentration (31.8–33.2% by mass) move together and both need to fall within range.
- Purity — trace metals, phosphate, aldehydes — is a separate question from concentration and needs laboratory testing to confirm.
- A genuine specification sheet states urea content, density and impurity limits explicitly, batch by batch.
- Don't mistake AdBlue's water content for dilution — it's the specification working as designed.
