Low oil pressure

I noticed while driving last week a low coolant light came on. My mother's house was a couple blocks away so I quickly went there. It never ran hotter than normal, however I noticed my oil pressure was at 40 on the gauge and it normally runs higher. I added water to the radiator which wasn't very much so I'm guessing it barely tripped that sensor. I looked around for a water leak but couldn't see any. So, I focused on the oil issue. I turned off the motor and checked the oil which was at the proper level. I cranked it back up and at a good rev up the pressure gauge wouldn't crest that 40 mark. So, I turned it off and left it there and am trying to determine if it's the pump or maybe the o ring on the pickup tube. Any input on this dilemma is greatly appreciated. Thanks. Oh, and upon checking oil I did notice the dip stick was warmer than normal.