Why Using Rainwater to Wash Your Car is Not Advisable

Filipinos love washing their cars in the rain, and why not? Rainwater is free, and you can easily clean an entire vehicle in a half-hour’s worth of drizzle. But there’s a reason why car washes and professional detailers use pressurized tap water and not rainwater to wash a car. In some cases, experts use de-ionized water as a final rinse before drying the car with a microfiber cloth, and there are reasons for this.

Is rainwater clean?

Unless you have a mobile laboratory to test and verify the cleanliness of rainwater, multiple environmental hazards can effortlessly turn fresh rainwater into something unclean or potentially hazardous. Furthermore, air pollution caused by nitrogen oxides, volatile organic compounds, benzene, sulfur dioxide, and carbon monoxide from tailpipe emissions, manufacturing facilities, and power plants will turn ordinary rainwater into acid rain.

What is acid rain?

When factories spew out sulfur dioxide and other contaminants, the emissions turn into nitric acid and sulfuric acid in the atmosphere. These nasty compounds can travel for thousands of kilometers before falling to the ground as rain or snow.

And here lies the problem. When acid rain falls on your car and evaporates, only the water goes away, and the acid remains on the paint. See those water spots or blemishes on the paint after rainwater evaporates? Those nasty deposits can eat their way through your car’s clear coat, eventually causing pits, mars, or damage to the finish.

Furthermore, the damage is irreversible through repeated washing, and you’ll need to decontaminate, polish, and wax the paint extensively to restore the finish. In some cases, you’ll need a complete paint job to fix the problem, which we all know costs a lot of money these days.

Is rainwater harmful to my car?

Falling rain can easily wash off excess dust, dirt, and mud from your vehicle, but you shouldn’t count on rainfall to make your car squeaky clean. Even the rainwater you collect after a heavy downpour will still contain heavy metals and pollutants that can induce scratches, swirl marks, and spots on the paint. For this reason, rainwater is not advisable to use when washing your car, especially if you have a black or dark-colored vehicle.

In short, rainwater is not harmful in the sense that it will destroy your car after a heavy downpour. However, repeated exposure to acid rain combined with neglect will hasten the deterioration of your car’s exterior, which in turn will also affect its resale value when selling your vehicle.

What should I do to my car after it rains?

We admit it’s hard to maintain a clean vehicle in Philippine tropical weather, especially during the rainy season. But there are certain things you can do to protect your vehicle’s exterior from acid rain, salt, and contaminants after a heavy downpour.

• Of course, your best recourse is to wash the vehicle with water and car shampoo. But if you don’t have time, the least you can do is rinse the car with tap water after it rains. Use a garden hose and spray clean water all over the exterior to remove rain contaminants and excess dirt.
• Pay attention to the windows and windshield. Try cleaning the windows and glass with a microfiber towel while rinsing the vehicle with water. Your car may be dirty, but at least it has clean glass to help you see better when it rains. Don’t forget to clean the wiper blades while you’re at it.
• After rinsing the exterior, spray clean water under the fenders and wheel wells. Excess dirt, mud, and salt can easily corrode metal parts in the undercarriage.
• Park your car in a shaded area or garage whenever possible. Exposing a wet vehicle to the hot sun will stimulate ugly water spots on the paint.
• Remember to wash your car with water and car shampoo at least once a week during inclement weather.

What is de-ionized water?

De-ionized water is no different from distilled water. The difference is the purification process. Whereas distilled water undergoes distillation to eliminate calcium and other hard minerals from the liquid, de-ionized water utilizes an ion exchange filter to remove calcium, iron, magnesium, and other negative ions. The de-ionizing process exchanges those negative ions for hydrogen (positive charge ions).

Professionals use purified water like de-ionized or distilled water as a final rinse to prevent hard water spots on the paint surface. In addition, de-ionized water dries quickly and makes it easier to dry an entire vehicle. Although car washes that use filtered water are far and few in the Philippines, the practice is slowly gaining traction among local detailers.