Generally, it is **not recommended** to use pure purified water, especially types like distilled water, as the sole coolant in your vehicle's cooling system, as it can lead to significant damage over time.
## The Role of Coolant in Your Vehicle
Your vehicle's cooling system is critical for maintaining the engine's temperature. The fluid circulating through it, known as coolant or antifreeze, is typically a mixture of antifreeze concentrate and water. This mixture serves several vital functions:
* **Heat Transfer:** Efficiently moves heat away from the engine.
* **Freeze Protection:** Prevents the mixture from freezing in cold temperatures.
* **Boil-Over Protection:** Raises the boiling point to prevent overheating.
* **Corrosion Protection:** Contains additives to prevent rust and corrosion within the system components (radiator, water pump, hoses, etc.).
## Why Purified Water Can Be Problematic
While water is a necessary component for heat transfer, using certain types of highly purified water on their own or even in mixtures can be detrimental. The issue lies in their chemical properties when in contact with the various metals found in a cooling system (like aluminum, copper, iron, etc.).
### The Risk with Distilled Water
Distilled water is a common example of highly purified water, stripped of minerals and ions. This purity makes it unstable and 'hungry' to absorb ions from its environment. According to the provided reference, **as it chemically removes electrons from the metals of cooling system components, distilled water eventually does extreme damage that could lead to cooling system failure**. This process, sometimes referred to as its "aggressive" nature, causes corrosion and weakens the metal over time.
## What Type of Water *Should* You Use?
Coolant systems require a balance. Plain tap water contains minerals that can cause scale buildup and corrosion. Highly purified water like distilled water can also cause corrosion by actively pulling ions from the metal. The solution is using the right type of water mixed with a quality antifreeze concentrate containing protective additives.
### Recommended Water for Coolant Mixtures
The reference suggests **softened water**. Softened water has undergone a process to remove hard minerals like calcium and magnesium, reducing the risk of scale buildup associated with tap water. However, unlike distilled water, it may still contain other dissolved salts, making it less aggressive towards metals than pure distilled water.
Other commonly recommended water types for mixing with antifreeze concentrate often include:
* **Demineralized Water:** Similar to distilled water in low mineral content, but processed differently. It's often considered suitable by coolant manufacturers.
* **Deionized Water:** Another form of highly purified water, also typically considered acceptable when mixed with proper antifreeze.
The key is that when mixed with the appropriate antifreeze concentrate, the concentrate's inhibitors protect the system from corrosion, mitigating the aggressive nature of highly pure water or counteracting the mineral content of slightly less pure options like softened water.
**Always check your vehicle's owner's manual or the coolant manufacturer's instructions** for the specifically recommended type of water to use when mixing coolant.
## Best Practices for Your Cooling System
To ensure the longevity and proper function of your vehicle's cooling system:
* **Never use pure water (purified or tap) as the sole coolant.** It lacks freeze/boil protection and corrosion inhibitors.
* **Avoid using plain tap water** due to its high mineral content, which causes damaging deposits and corrosion.
* Always use a proper antifreeze/coolant concentrate mixed with water at the recommended ratio (often 50/50).
* Be cautious with highly purified water like distilled water when using it for a mix, as highlighted by the reference warning about **extreme damage** if used improperly or on its own.
* Consider using **softened water**, as suggested in the reference, or demineralized/deionized water when mixing coolant, in accordance with manufacturer recommendations.
Consulting your vehicle's manual or a trusted mechanic is always the best approach for specific coolant type and mixing instructions.
| Water Type | Suitability for Pure Use | Suitability for Coolant Mix (with Antifreeze) | Reason |
| :------------- | :----------------------- | :-------------------------------------------- | :---------------------------------------------------- |
| Tap Water | No | Generally No | High mineral content, causes scale & corrosion |
| Distilled Water| No | Use with Caution / Check Manual | **Chemically removes electrons, causes extreme damage** |
| Softened Water | No | Recommended (Ref.) | Lower mineral content, less aggressive than distilled |
| Demineralized | No | Often Recommended | Low mineral content, less aggressive than tap |
