cool down for what? it's not gonna add any hp to your car..

it's tiny bit effective as super cheap idea.. however compared to real upgrade, it's not. ok la.. for fun..

cool down for what?
how much water you can carry, and how often you want to spray the radiator?
and you want to spray by a swirch all the time?
what gains you get?
btw, it will only make your radiotor prone to leaking faster because material will warp easily (hot and cold contact) which creates stress to the metal + steam.

to me I think not productive at all. just my 2 cents ya....

Caution, this doesn't has anti-freeze. But I guess doesn't matter in Malaysia.

Use the bonet damper. It will raise up the hood a bit so hot air can come out and keep engine bay cooler when stop. When driving it can give better airflow.

you need run the pump consistantly to make a noticable effect

I did this before on my mpv to keep ac cold when waiting kids 2hrs in parking, 1.5L bottle finish in i think 10mins.... barely noticable difference in my situation.

But if your situation is moving vehicle & heat build up in engine bay, exhausting the heat would be first step instead of trying to cool down the heat.

ktek can look for intercooler sprayer kit, quite common mod
some guys eventually added 45L tank for this purpose, that's 45kg of water

but, that's for intercooler, not so much for radiator, because the coolant in the radiator is liquid with a much higher latent heat capacity than air (intercooler). To remove heat from that, you need more CFM as mentioned above, to carry the heat away.

ideally AC condenser is liquid, but if the compressor is less than effective it can be pressurized vapor also
and again.. spraying water to alu can shorten its lifespan, and those things are 300 ringgit above to replace

I'd suggest you add an electric fan to pull more air through the rad and condenser

my Exora turbo, can see significant difference with the AC fan running vs without
I use OBD to take temp
with AC, it's 85C, without AC, 92C...

Route the evaporator water to your tank? Or let it drips to your condensor .