The river side of Glastonbury gets fog and heavy dew for a good part of the year. If your car sits outside near the water, it is getting wet almost every night whether or not it rains.
Most people treat that as harmless. It is the most common cause of the faint rings on a car that is otherwise well looked after.
Dew is not distilled water
Water vapour needs something to condense onto. It uses airborne particles — dust, pollen, whatever the air is carrying — so every droplet forms around a nucleus and collects more as it sits.
Then the sun comes up, the panel warms, and the water evaporates. The particles it was carrying do not. They are left exactly where the droplet sat, as a ring, and the process repeats the next night on top of the last one.
On a car parked outside all summer that is roughly a hundred cycles of the same deposit in the same places.
Why it gets baked in
The dangerous version is dew that dries on a panel already warming in direct sun. A droplet acts as a lens, and the combination of concentrated minerals and heat can etch the clear coat rather than just sitting on it.
The difference between a deposit and an etch matters, because one washes off and the other needs machining. A deposit sits above the surface and you can feel it as roughness. An etch is a dimple in the surface and stays visible on a clean, dry, cool panel.
Sprinklers are worse than dew
Anyone with irrigation near a driveway will recognise this. Lawn sprinkler water is hard, meaning high in dissolved calcium and magnesium, and it lands on paint in far greater volume than dew.
Baked onto a hot panel through a summer, sprinkler spotting is the single most stubborn water marking we deal with, and it frequently needs polishing rather than washing. If a sprinkler head is reaching your parked car, moving the head is the cheapest detailing decision available to you.
What removes it
Fresh deposits come off with a proper wash and a decontamination — clay shears off the bonded mineral residue and the paint goes back to smooth. That is part of our exterior detail at $145 and our full detail at $275.
A sealant afterwards genuinely helps here, because water beads and rolls off a sealed panel instead of sitting in a flat droplet with time to deposit.
Where it has etched, levelling it is paint correction at $449. We will tell you which one you have by feel and by looking at a dry panel, before you commit to either.
The free habit
If the car is wet with dew and you are about to leave, driving it dry at speed is better than letting it evaporate in place. The water blows off rather than evaporating, and it takes most of the dissolved material with it.
That costs nothing and it prevents most of this.