Hi Cristi, the water/coolant is added in the radiator which can be filled if you remove the gas tank cover which is quite simple to do: first remove the gas cap, then remove the metal gas cap ring which is held in by the two 5mm hex-key bolts at the 7o´clock and 5o´clock positions, remove the seat and directly under the crotch area remove the two screws from the gas tank cover, then remove the two screws from the gas tank cover near the forks/handlebar end of the cover. Now the gas tank cover will lift off. You can now see the gas tank which is turned vertical unlike most bikes and directly in front of the seat, in front of it is the air induction box and directly in front of it is the radiator cap where you can fill with coolant and water. I have always been told to use 5-W-20 Castrol Oil for these bikes and the oil filler cap is the black cap just above the foot break pedal. Anything else? Enjoy, Don Metzeler