If water gets into diesel fuel, it can cause several problems, including:

1. Reduced engine performance: Water in diesel fuel can disrupt the combustion process, which can cause the engine to run poorly or stall. Water can also cause corrosion and damage to the engine’s internal components, which can lead to reduced power and increased emissions.
2. Clogged fuel filters: Water can cause the fuel filters to clog, which can restrict fuel flow and cause the engine to run poorly or stall.
3. Corrosion: Water can cause corrosion in the fuel system, which can lead to leaks, fuel injector failure, and other problems.
4. Microbial growth: Water in diesel fuel can also lead to the growth of microorganisms such as bacteria, fungi and algae. These microorganisms can cause the fuel to degrade and can clog fuel filters, fuel lines and injectors, leading to engine problems.
5. Emissions issues: Water in diesel fuel can also cause increased emissions, which can lead to increased pollution and potential legal issues.

To avoid these issues, it is important to use clean, high-quality diesel fuel that meets industry standards and to regularly maintain the fuel system. This includes regularly checking the fuel filters, draining any water that may have accumulated in the fuel tank, and checking for any signs of corrosion. If water is already in the fuel tank, it is important to drain the tank, then check and replace the fuel filters, and check the entire fuel system for any signs of damage or corrosion. It’s also recommended to have a regular check-up and maintenance of the fuel system, to avoid water and other contaminants getting into the fuel tank.

In summary, water getting into diesel fuel can cause several problems such as reduced engine performance, clogged fuel filters, corrosion, microbial growth and emissions issues. To prevent these issues, it’s important to use clean and high-quality diesel fuel, have a regular maintenance check, and drain the fuel tank if water is already present.