Comment by jacquesm

If you have more water in the fuel than you think you do (there always is some due to condensation in the tanks) then you might be able to reach your destination but you'll be burning more 'fuel' than your original estimate would have you believe because there is less power per unit weight of (contaminated) fuel.

This is fairly common in GA and there are cases where it has happened in scheduled flights as well. That's why fuel sampling is common practice.