Best advice is to take your time and don't jump to conclusions.
Water in the oil can get there several ways. Need more information to advise the best way to proceed.
Has the truck been sitting for a long time or was it running regularly?
How much water? did you drain the oil?
Was the radiator full or empty? If there is antifreeze in the radiator is the water in the oil antifreeze or clear water?
If it has been setting and not running, have you tried to start it yet?
Always try to determine the real problem and the most likely cause before you take something apart. That can save you a lot of work and money.
