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.