Water checks - How To

The radiator and water bottles generally have guages on the side of the plastic containers to indicate how much liquid is present. checking these levels should always be done with the engine is cold, because of the expanding properties of the liquids involved. Once you have checked the levels against the indicator removal of the bottle caps may not be required depending on how much liquid is present.
Some newer water radior header tanks have dip sticks in the same way as the oil indicators shown here In which case removing the cap will show the level of the liquid present. Old style radiators may not have either system in which case removing the cap is the only way to find out how much water is currently present. WARNING, with the expansion properties of the liquids used you should never remove the cap of a radiator when the engine is hot.
Top up if required.