You primarily add water to your car's windshield washer fluid reservoir and, in some specific cases, the coolant system's overflow tank. Never add plain water to the windshield washer tank in freezing climates, as it can crack the reservoir. For the coolant system, a 50/50 mix of antifreeze and distilled water is standard; using only water is an emergency fix, not a long-term solution.
The most common place to add water is for your windshield washers. The windshield washer reservoir is typically a white plastic container with a cap marked with a windshield/water symbol (🔵). It's usually located at the back of the engine bay, near the fender. In winter, use a premixed washer fluid with antifreeze properties to prevent freezing.
For the cooling system, the coolant reservoir (or overflow tank) is a translucent plastic container with "MIN" and "MAX" level lines. The cap is often marked with a warning symbol. Only open this cap when the engine is completely cool to avoid being sprayed with scalding hot coolant. While a 50/50 mix is ideal, adding a small amount of distilled water (not tap water, to prevent mineral buildup) is acceptable if the coolant level is slightly low.
Here's a quick reference table for the fluids involved:
| Location | Fluid Type | Purpose | Key Precaution |
|---|
| Windshield Washer Reservoir | Washer Fluid (or summer blend water) | Cleans windshield | Use antifreeze washer fluid in winter |
| Coolant Overflow Tank | 50/50 Antifreeze/Water Mix | Regulates engine temperature | Only open when engine is cold |
| Battery | Distilled Water (for serviceable batteries only) | Maintains electrolyte levels | Modern batteries are typically maintenance-free |
Your car's battery is another component that might need water, but nearly all modern car batteries are sealed and maintenance-free. Only some older or specific types of batteries have removable caps to add distilled water.
