Does anyone know of a chemical indicator that changes color when water is introduced

Just now, Matt Wieland said:

Does anyone know of a chemical indicator that changes color when water is introduced

Anhydrous cobalt chloride. Goes from blue to pink and is often used to colour dessicants such as silica gel, so you know if they are still active or not. 

Because Cobalt salts are carcinogen, it's not available. Water free CuSO4 is white and change to blue if water is present.

4 minutes ago, chenbeier said:

Because Cobalt salts are carcinogen, it's not available. Water free CuSO4 is white and change to blue if water is present.

Really? These people are still selling indicator paper impregnated with CoCL2. https://uk.vwr.com/store/product/2994210/cobalt-ii-chloride-paper-in-strips-for-detection-of-water-vapour

looking for a "unique" chemical or maybe a combination of chemicals to make it "unique"

also looking at chemical that could be seen under UV only when exposed to H20...any thoughts?

27 minutes ago, Matt Wieland said:

looking for a "unique" chemical or maybe a combination of chemicals to make it "unique"

also looking at chemical that could be seen under UV only when exposed to H20...any thoughts?

What do you mean by unique in this context? If you mean novel, i.e. one nobody knows about yet, then obviously we can't help you.  If you want a UV absorber that only absorbs in a hydrated form, then I'm sure there must be candidates. Possibly some of the organic dyes even. But hard to think of offhand. 

I don't understand the thread title.  Isn't it about chemicals that change color when mixed with water??  Should I start titling all my threads "Paul" ?  

Copper changes color in water.  But it's kind of slow...

Yeah, I think a litmus paper would do the trick! It's a cool, easy-to-use chemical indicator that changes color when water is introduced.

1 hour ago, TheVat said:

I don't understand the thread title.  Isn't it about chemicals that change color when mixed with water??  Should I start titling all my threads "Paul" ?  

Copper changes color in water.  But it's kind of slow...

You could start a thread called "Gloss". 😁

4 hours ago, Matt Wieland said:

looking for a "unique" chemical or maybe a combination of chemicals to make it "unique"

also looking at chemical that could be seen under UV only when exposed to H20...any thoughts?

Looking at the absorption spectrum of liquid water ;

Doesn't this make it essentially black to UV? Seems to defeat the object. 

Water is black to UV with a wavelength below about 200 nM.
But so is air, so it doesn't usually matter.