It's the hard minerals in the water (and some other stuff that makes it totally undrinkable!). Get a small bottle of olive oil, the fragrant stuff on the shelves in the supermarket, colour of urine. Just rub this on after your shower. Feels nice, not a strong perfume at all, stops irritation.

I dont think it's a good idea to bathe with the water here. best to shower. the idea of soaking in the filthy polluted water

depends which city and the weather. if your skin is itchy you are using hard water. so put on some lotion. you might be allergic to some of the soap but i guarantee its the hard water and weather.

Never had a problem.

From what you say, there are two possibilities :
1) the water : because of the hard minerals inside the water and naturally the proportion of hard minerals in it. Some locations are better equipped than others.
2) the shower gel : I noticed that some shower gels (even Foreign brand) are extremely bad for the skin compare to the one sold in Western countries and may provoke some skin allergies. I got my penis turned to red for a couple of day because of one of them.

So make some experiment : to take shower without any shower gel or soap, to take shower in a friend's apartment, then you may find the cause of your skin irritation.

By the way, in Shanghai, the Water company has recently stated in a newspaper that the water in Shanghai is drinkable........STOP.....don't rush to taste it......
It may possible, but if the pipelines are still rusty and old, then whatever drinkable water you have at the origin will eventually turn undrinkable.

Since coming to China, I too have had this problem after showering.  However it happens to me after I've sweat too.  It also only happens during the two most humid months of the year, June and July.  It makes those two months a loving hell where I can only go outside for short trips to the market and even those usually end with intense itching.  It usually lasts an hour but in extreme cases longer.  The daily pain together with me being cooped up inside everyday is putting me into a depression.  In Winter, I won't even have a single incident.   Can drinking the water cause my sweat to do this?  Is it the air? 

  I used to get this badly, tried every lotion and powder. After only FIVE YEARS it stopped. Wish I knew about that olive oil / piss wipe stuff Daqing Devil suggested getting when I first arrived here.

There are a ton of skin allergies.  Usually babies get this stuff because their skin is so soft and new.  Hmm, Buffalo Bill, is that you?  Kidding.  Talcum powder (baby powder) reduces itching.  Actually, we use this other stuff for our daughter and it worked really well for itching, irritation, swelling, diaper rash, other rashes, etc.  It is called, "Fu fang zi cao you."  If you look up the term "diaper rash" on google translate and show them the pinyin above, then you should be good to go.  I wish I could post a picture.  They may have a website.  

no .......................... never happened to me............you just paranoid of everything chinese.....................my friend take a warm shower and calm down.......LOL