* Diesel fuel specifications: Different fuel standards (e.g., ASTM D975) will have different water tolerance limits. These limits are often expressed as a maximum *percentage* of water by volume, not ppm. Even then, the allowable percentage might be quite low, and exceeding even a small amount can cause problems.
* Fuel system design: Modern fuel systems are generally more sensitive to water contamination than older ones. High-pressure common rail systems, for example, are particularly vulnerable to the damage that water can cause.
* Environmental conditions: Cold temperatures can lead to the formation of ice crystals, even with relatively low water content, causing fuel filter blockage.
* Fuel type: The specific formulation of the diesel fuel can impact its tolerance for water.
While ppm (parts per million) is a useful measure for small concentrations, you're more likely to see water content limits expressed as percentages (e.g., <0.05% water) in diesel fuel specifications. To convert a percentage to ppm, multiply by 10,000.
In short: Instead of searching for a specific ppm limit, you should consult the relevant fuel specification for the diesel you are using. Even small amounts of water can be problematic; aiming for the lowest possible water content is always best practice. Regular fuel testing is recommended for ensuring quality and preventing problems.
