Car should be OFF. If it CAN be refilled you would remove the caps located on top of the battery. Carefully add distilled water until water level is full but not overflowing. Replace caps. Wipe off any spilled water. Do NOT get any water from battery on your clothes, skin or eyes. Do NOT smoke while refilling your battery - it could explode!
distilled water
The reason for the battery to loose water is due to the heat, in which the water will evaporate... that is why when you refill water they say to only use distilled water, as the acid is now much more concentrated. A battery that is being overcharged will also loose the fluid.
During the summer months, the battery acid can evaporate (unless you have a Maintenance Free" battery. Open the caps on your battery. You should see water directly beneath the opening. If you see the metal splines inside the battery, then you need to refill it with DISTILLED water. Don't use tap water!
in your but
It means, that you have to refill oil and cooling water.
Yes, if the battery is not a sealed unit and then only add distilled water and never add tap water.
add water and charge the battery
Car batteries are filled with sulfuric acid, not water. The battery fluids get "topped up" with distilled water if they get low.
You will shorten the life of the battery. Only add Distilled water to a battery.
If you can see the plates in the battery add distilled water to top it off.
Add Distilled water to the battery and then charge it fully with a battery charger. Do not add tap water.
No, you should only add distilled water to an auto battery.