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To answer ur query firstly i would make you aware to go through the user manual of you car. Ideally most of the cars use water and collant mixture. Water is the major component for cooling the radiator. Collant is used with water to prevent corrosion, and using collant reduces the temprature of the mixture to some extant.
The collant reserviour should be checked regularly if the level of liquid in the reserviour is between the min and max levels.
This helps in checking if there is leak in the system. Check your user manual if the water used should be regular water or distilled water.
Top it up if the level reduces. Generally the mixture will be 50% water - 50% coolant, or 70% water - 30% coolant. For the recomemded mixture proportion check with the user manual of your vehicle.