Why Ceramic Coatings CAN’T Prevent Hard Water Spots

Hard water spotting on a ceramic coated car caused by a sprinkler system with heavy mineral water.

By Christopher Brown of OCDCarCare Los Angeles – OCDCarCare.com – 6 July 2019

Most automotive ceramic coatings feature hydrophobic water behavior. This is the ability of a surface to quickly and effectively shed water. Extreme water behavior is great feature of ceramic coatings and has become a huge industry selling point due of the self-cleaning effect and ease of washing aspects.

While coatings are a valuable and helpful ally in the fight against topical contamination and hard water damage– they are by no means a magical savior. So, no matter the marketing campaigns by companies or detailers, ceramic coatings and their hydrophobic properties, cannot guarantee any protection against water spotting.

Because, well…. NO-THING Can.


Two Words: Science & Chemistry

The scientific fact that minerals in water will deposit themselves into automotive paint, if allowed to sit on paint long enough, is inarguable. Because the primary factors that most influence:

  • the creation of 
  • and vulnerability of vehicle surfaces to

water spotting are much greater contributing factors than what a surface’s topical protection is.

It’s simple uncomplicated science, yet the information is seldom discussed. This is because many manufacturers and businesses prefer to market coatings as a surface solve-all type of solution– WHICH THEY ARE NOT.

Hydrophobics HELP Protect Against Hard Water Spots– THEY DON’T PREVENT THEM 

Hydrophobic properties grant ceramic coatings the ability to: help keep vehicles clean for longer, allow them to shed water, and enable very quick and simple car washing. These beneficial attributes aid in vehicle enhancement and functional lifestyle benefits. For deeper information into the science behind hydrophobics, please reference the article: The Science of Detailing Surface Energy.

The positive attributes of a ceramic coating’s hydrophobic properties primarily occur when a vehicle is in motion–air moving water. Essentially, hydrophobics assist in moving water or contamination off surfaces as fast as possible to help eliminate damage from occurring. But, even the best coating, featuring the most insane water behavior, cannot combat mineral deposits if the vehicle sits still and water dries on surfaces.

Additionally, gravity greatly enhances the chance of water falling off vertical panels. However, horizontal panels, those parallel to the ground – which are often flat or concave – are not so fortunate. Horizontal panels, especially on a stationary vehicle, are immune to gravity and have no means of shedding water. This leaves them much more susceptible to water drying on the surface and depositing minerals.

Therefore, it is CRICITCAL to NEVER allow standing water to sit and dry on vehicle surfaces.

The Dangers of Hard Water Spotting to Vehicle Surfaces

Sure, water spots are unsightly blemishes upon finishes, particularly on darker colored vehicles. However, the potential chemical hazards of water spotting are of far greater concern than displeasing white markings.

If water contains a high concentration of minerals and harsh chemical contaminants it may inflict great harm upon vehicle surfaces. Combine this with automotive paint that is on the vulnerable end of the spectrum and it may cause issues such as deep etch markings, discoloration, and precursors to rust (oxide contamination). This is because the water acts a transport mechanism, moving contamination into porous automotive paint systems.

If water spots occur and the vehicle’s paint repeatedly heat cycles (heat up and cool over many days, weeks, or months), the water spotting may seep further down into the paint. Because, when panels are fully swelled open by heat — at their most vulnerable point– any minerals contacting the paint have the greatest likelihood to sink further down into the paint or fuse within the paint’s matrix.

Upon first detection of water spots, it is critical to IMMEDIATELY wash the vehicle.

This will likely remove any new minerals sitting on top of a paint system which haven’t had time to fully fuse into the paint.

The Scientific Explanation of Automotive Water Spots

Hard water spots occur when water dries on a surface. When water evaporates, mineral deposits are left behind. Seems simple enough—but there’s a bit more to it.

If a vehicle remains stationary, and water partially or fully dries on the surface, nothing can be done to prevent the minerals from seeping into the paint. If the panel is cool, then water spotting may not occur. However, if the painted surface is HOT when the water evaporates then paint’s porous structure swells open and reaches maximum vulnerability. Sometimes the panel is hot before water contact, and other times the panel heats with water already on top. Either way, the minerals can seep DEEP into the paint, even past fully cured ceramic coatings.

When the paint’s pores open fully, minerals and other chemical contamination can very easily stick to and embed within the vehicle finish. So, when water evaporates from a hot panel, the minerals are left behind to embed themselves DEEPLY into the paint.

Some common minerals contained within water, such as calcium and magnesium, are extremely alkaline. A high concentration of calcium in water may cause etching to some paint systems. The depth of the etching depends on the type of minerals, the overall concentration levels of minerals within the water, and the length of time those corrosive mineral agents dwell on top and within the paint.

Defining Water ‘Hardness’ Measurements

The term “hard” or “soft” water refers to the level of minerals concentrated in water, as measured in milligrams per liter (mg/L) or PPM – parts per million. Often these numbers are publicly available for reference from local utility officials. Otherwise, a simple water hardness test strip kit will quickly reveal the level of dissolved minerals contained in any water source.

The classifications of water types are as follows:

  • Soft: 0-17mg/L (ppm)
  • Slightly Hard: 17.1-60mg/L (ppm)
  • Moderately Hard: 61-121mg/L (ppm)
  • Hard: 121-180mg/L (ppm)
  • Extremely Hard: 180mg/L (ppm) and Higher.
  • RIDCULOUSLY HARD: Las Vegas, NV is 270ppm. Some Cities in Arizona and the Rocky Mountains can even read past 450ppm.

Automotive Water Spot Creation Variables

The FIRST variable majorly influencing whether a vehicle is more or less prone to the formation of hard water spots is the paint’s chemical formulation. Think of it like spaghetti sauce staining a linen shirt. IF the color of a cotton shirt has low pigmentation, say white, then it is already vulnerable. The chances of removing the stain completely depend on the amount of time the densely pigmented red sauce is allowed to dwell on the shirt. If the sauce is removed moments withing staining it is relatively easy to fully remove. However, if the stain is undetected and allowed to seep into the cotton weave and fully dry, then sits in the bottom of the laundry basket for a week, then good luck. Some automotive paint systems are similar to various types shirt materials in terms of their vulnerability. Some paint systems contain a low amount of solids and therefore are more vulnerable to the effects of heat and chemical contamination. On the other hand, paint systems with a high solids content offer far greater protection overall.

The SECOND group of factors influencing water spotting are the water’s mineral and chemical composition and their concentration levels. The ability to create Damage via Water Spotting or Chemical Damage to paint systems is directly linked to: A) The types and combinations of minerals and chemical contaminants contained within the water. And B) The concentration levels of those minerals or chemical contaminants within the water.

The THIRD variable of water spot creation is HEAT. More specifically, the temperature of vehicle panels or the environment’s ambient temp during water evalporation. Heat acts as a catalyst to the paint system causing more vulnerability– therefore magnifying the impact of the waters mineral concentration. If a panel is already HOT (140°F – 60°C) before water contact, that is the worst recipe for quick and deep water spotting.

In the heat of direct sun exposure, with atmospheric temperatures between 95°F and 110°F (35-43.5°C) panels can routinely reach surface temperatures of 190-212°F (87-100°C).

In these extreme conditions, the paint is most vulnerable, because the heat has swelled the porous paint structure to fully open. So any water contact to these HOT surfaces results in near instant water evaporation. This essentially injects the minerals and chemicals contained within the water directly into the paint’s porous structure.

Even if a car isn’t in direct sunlight, ambient environmental temperatures of 95°F(35C) or higher still cause paint swell and heighten the chances of water spot creation with water contact.

Therefore, the combination of: A) a vulnerable paint system, B) mineral and chemical heavy water, and C) HOT vehicle panels, equals a surefire chemical recipe for disastrous hard water spotting. Some automotive paint systems are so vulnerable to chemical agents that ceramic coating enhancements may only slightly improve the overall chemical protection.

Vehicle Water Spot Protection Strategy

No current paint system or paint treatment, including ceramic coatings, may guarantee complete protection against water spotting.

There is no solve all water spot protection for automotive surfacesNo Matter What Certain Coating Manufacturers or Detailing Companies Claim.

It’s just a impossibility within the known physical universe we inhabit.


The best protection against vehicle hard water spotting is a STRATEGY.


If water is not allowed to dry on a vehicle’s surface, then water spotting may be avoided completely. Additionally, using mineral free water during car washes (including Waterless and Rinseless wash methods) will ensure vehicle surfaces remain unspotted. De-ionizing filtration systems remove most all minerals and deposits from water such as calcium, sodium, iron, copper, and sulfates.

Top Tips to Avoid Vehicle Hard Water Spots

  • DON’T Let Water Dry on Vehicle Surfaces: Remove as Soon as Possible
  • Only Wash Cool Vehicle Panels
  • Avoid Washing in Direct Sun: Wash Vehicles in Shaded Areas Only
  • Immediately Dry Vehicle After Washing
  • Avoid Parking Near Sprinklers or Irrigation Whenever Possible
  • If Incidental Water Contact Occurs, Dry Panel ASAP
  • If Vehicle Dirty and Rain Occurs, Wash Vehicle ASAP
  • Purchase a Water Softening System or De-Ionizer for Car Washing
  • For Waterless or Rinseless Car Washing: Mix with Distilled Water
  • If Hard Water Use is Necessary: Wash Vehicle in Early Morning or Late Evening
  • In SUPER HARD Water Areas: Apply a Topical Spray Sealant (same Product Line) on Top of Coating for Added Protection

Water Spot Removal Techniques:

Upon first detection of water spotting, immediately wash the vehicle to remove the maximum amount of minerals possible from surfaces.

Often times, a thorough car wash will remove light or freshly made water spots by cleansing the surfaces and of hard mineral deposits before they set up.

Stubborn Water Spot Removal Methods After Washing

If washing does not entirely remove water spots then move to spot treating areas with distilled white vinegar. The vinegar’s acidity works to break down and loosen the minerals for removal with a microfiber towel.

Apply the vinegar liberally to a microfiber towel and then apply evenly to water spots. Allow vinegar to dwell for 2-4 min. Then gently wipe at the spots with the microfiber towel. If spots are stubborn, apply a second time and allow the vinegar to dwell 6-8 min before wiping.

If Vinegar alone does not work, try mixing in some fresh juiced and strained lemon juice with the vinegar in a 50/50 ratio. Apply the mixture and allow it to dwell for 3-4 Minutes before wiping with a microfiber towel.

For a heavier concentration of water spots allow the mixture to dwell for 5-7 min, then liberally apply more vinegar mixture to a microfiber towel before wiping the spots with light to medium pressure.

For stubborn or heavier mineral deposit removal, a dedicated automotive water spot removal product may be necessary. The majority of these are heavily acidic in nature, therefore wear protective goggle and gloves during use. Also, take caution to ONLY apply the product to surfaces indicated as safe on the product label.

NOTE: After any acidic surface treatment, make sure to thogoughly flush all panels with water or a waterless wash solution.

Removal of Severe Hard Water Spots

Some hard water spots cannot be removed via topical treatments. Paint Polishing may be the only action for removal of this severe level of hard water spotting. These are identified by their: extremely heavy mineral deposits, ultra deep position within the paint’s structure, or even by mild to sever surface etching.

Often a light paint correction is enough to remove spots—however the more severe and concentrated the spots– the more aggressive the polishing necessary. Seek out a local reputable detailer to perform such services. After the removal of hard water spots, make sure to reapply the topical protection that matches the remainder of the vehicle panels.

If water spots were detected immediately after ceramic coating application, the problem may be a different sort of water spot issue completely. This complex removal procedure was explored in a previous OCDCarCare Los Angeles Detailing Article.


Ceramic Coatings, depending on their chemical composition, offer the best current protection for vehicle surfaces against contamination and water spots – due to their increased solids content, chemical protection, and hydrophobic properties. However, they are NOT a solve-all savior of surface protection. And they should not be sold in such a fashion to uneducated vehicle owners.

Sure, some ceramic coating manufacturers may even outright claim their products prevent water spots. Don’t believe the marketing speak of over-hyped protection. The proof is in the chemistry and the practical aspects of how coatings function to protect paint and vehicle surfaces… Information some coating manufacturers either don’t understand themselves or don’t want you to know, understand, or investigate.

Keep on Buffin’

© Christopher Brown of OCDCarCare Los Angeles – OCDCarCare.com – 2019

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Christopher Brown

Christopher Brown operates OCDCarCare Los Angeles, specializing in paint correction, ceramic nano coatings, and Auto Detailing Training Courses.
His passion & dedication to car care lead him to writing in-depth articles about detailing in order to share with the car enthusiast & detailing communities. This lead to detailing training courses designed to develop skills, confidence, and results, enabling detailers to increase quality, efficiency, and profitability.

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