Drain it..........water is bad on the fuel pump. If it gets past your filter/fuel water separator it will kill your injectors. It will also aggravate the growth of algae in your fuel tank.
A related story......
One day I stopped to help a guy in a PSD stranded on the side of the road. We pulled the cap on his fuel filter and it looked like milky pond water in the bowl. The guy had filled up one mile up the road. His truck was done and would not run.
While we were standing there waiting on tow truck a box van with a International DT466 diesel engine comes down the highway sputtering and died 50yrds away from us. He too had fueled up at the same station one mile up the road. I found out latter that due to the water contamination the fuel supplier had to pay to drain and flush the entire system on one of the trucks and replace the injectors. Don't know what happened to the other one.
Tbar