@Siena and other people with expertise/technical know-how

my friend just got an 04 passat that keeps showing "oil pressure, service manual and STOP". also, the car started over-heating and any time he updates the water, it over-heats in minutes.

any solution(s) as to how to get this problem fixed once and for all.

thanks!

If no "expert"has already tampered with it, first thing is to pull the DTCs because your check engine light is on.

Check your oil level, it a turbo engine(if it 1.8T) uses more oil than other cars to see if that is causing your oil pressure warning.
Feel your hoses to see if any has collapsed.

You should be using coolant instead of water, but if you are losing coolant you have a leak somewhere, either at radiator cap or pin hole leak on the hoses. If someone had removed thermostat you may have air poket in you system or bad water pump.

Do oil change with OEM filter and check your old oil for water/coolant(if non you are safe)

Your oil pressure gage should be read around middle point if high you might have too much oil in engine if low check oil level or pressure sender.