TS, it will get better over time. I was like you initially trying all sort of ways but eventually after few years, it seemed to have been better. I suspect the car washing and polishing of the glass once in a while removes it over time. Lately I'm using Rain X for the windscreen and it seems ok.

Since that day, i never used any watermark removal products.

I encountered exactly the same issue with my wife Estima 2-3 mths ago, bought the water stain mark removal liquid and applied on side windows + windscreen.

And voila, I hit the jackpot for the windscreen that the white mart was so so apparent where I could hardly see clearly when driving at night.  Then there was a guy in Skudai (I am from JB) offered to solve the problem for me.  He used 3-4 diff type of compounds to polish the windscreen for me.  Spent RM130 and my problem settled.

Expensive lesson.  I hope your problem is not too serious that not the entire windscreen is infected.  Else the glass specialist will charged quite a lot.  Mine was only infected at drivers area, about 10% of the total windscreen (estima has a BIG windscreen) and yet paid RM130 for the job done.

I also have the  white marks on the wiper area, but it was solved easily by polishing it. But, this does not solve my problem. Because, the chemical has eroded the glass, causing uneven surface on the windscreen. The bubbles can only be visible through the reflection on the screen. 

yup, that's why I said you need GLASS polish, not normal polish.

I also have the  white marks on the wiper area, but it was solved easily by polishing it. But, this does not solve my problem. Because, the chemical has eroded the glass, causing uneven surface on the windscreen. The bubbles can only be visible through the reflection on the screen. 

The acid watermark removal is never meant to be used on the wiper area of the front windscreen as there are scratches and stone chip. The acid will fill into the holes of the scratches and make it blurry. This is not the 1st time happened.

The remedy is to polish put the acid at the scratches by using heavy paint correction compound.
The pro will be using Meguair's m105 or Glass Compound such as Osren or CeriGlass

For Consumer - use the glass compound such as Soft 99 Glass Compound Z which is available at Brother's Kelana Jaya for about RM 30+.  If that's too far, you may use Autosol Metal Polisher in toothpaste that is available in any hardware shop or hypermarket. It may cause micro (tiny) scratch, not naked eyes visible but against sun light as it is not meant for glass.

Be prepared to rub and rub (many rounds) to see improvement.

If left uncorrected, the blurriness will disappear after 1/2 year to 1 year time depending on the taken to dilute acid from the scratch. If you cant's wait and want a quick solution and willing to pay, is to sent to the pro detailing shop and the normal charges are between RM 150-RM 250.

Normally, the acid is only used when the glass is heavy stained . Acid is the fastest but not the safest way to clear watermark on windows.

The above are based on actual experience when used a similar acidic product brought at hypermarket.

is it the rainbow kind of blurness and quite irritating at night?

I've used this Soft99 Glass Stain Cleaner to remove watermarks and 1 year old Ultra Glaco coating on my windscreens... Very good...

http://www.soft99.co.jp/english/products/c....html?pid=05066

You can also try Soft99 Glass Compound Z like what mot88 suggested... You can find it at Autobacs Klang or Eneos...

after use soft99 glass stain cleaner must use ultra glaco to coating?? if only use stain cleaner dunwan coating can?

Can but water won't bead anymore during rain just to let you know...