Hi

My diesel in my mitsubishi is contaminated. It is a pale black colour and I've been told it could be down to water in the tank. Is this a feasible explanation and if so, How do I rectify this?

Thanks for any help.

The black colour is more likely microbial growth. Believe it or not, some organisms can live in diesel fuel.
You could try some of the additives that are available, but they are best suited for maintaining a fuel system, not cleaning it.
You're probably going to need that tank and fuel system drained and professionally cleaned and treated.

CaptainRich is "dead on."