It is not recommended to put plain water in the engine coolant reservoir as a substitute for coolant. While water can temporarily help lower engine temperatures, it lacks the necessary additives to prevent corrosion, raise the boiling point, and lower the freezing point. If you must use water in an emergency, it’s best to replace it with the proper coolant mixture as soon as possible. Always check your vehicle's manual for specific recommendations.
If there is no risk of freezing , but it will weaken the strength of the antifreeze / water coolant mixture
In radiator or through coolant recovery tank
Engine coolant.
The water and coolant is put in the coolant reservoir for the location of this refer to the owners manual. It is best to do this when the engine is cold otherwise you run the risk of getting boiling water all over you. the mixture of coolant to water should be about 50/50.
You add coolant to the reservoir and in the radiator cap.
At the radiator or overflow tank. Do not add water, add coolant.
It is not suggested to put water in a Toyota Rav 4. The engine cooling system can get too hot and coolant is preferred. To pour coolant find the coolant reservoir and pour fluid until the max line is filled.
in the coolant resivor
When the engine is cool
If your car is leaking coolant get it fixed and put in the recomended coolant for your car. You should locate that info in the manual, also putting water in the winter is a bad idea since the water could freeze causing engine damage. I supposed you might be able to run it for a while in the summer with just water but get the leak fixed and put in the recomended antifreeze/coolant
Coolant recovery tank
In an emergency situation you can add water. But coolant contains anti-corrosive additives that prevent rust. Leaving plain water in your engine will eventually destroy it