What unit is used to express the maximum H2O limit for JP5 fuel under DFWD conditions?

• A. ppm
• B. mg/L
• C. percent
• D. pH

Answer: (A)

Fuels are regulated for trace water because even tiny amounts can cause problems in storage and operation. The unit parts per million is used to express the maximum water content in JP5 under DFWD conditions because it conveys very small fractions in a clear, density-independent way. One part per million means one water molecule for every one million fuel molecules, which aligns with the tiny quantities that standards tolerate. Other options don’t fit as well: milligrams per liter ties the limit to volume and density, making cross-fuel comparisons awkward; percent would imply a much larger fraction and lose sensitivity at the low levels typical for aviation fuel; pH measures how acidic the water is, not how much water is present in the fuel.