I do not think there is a right answer to this

Some people will say that the first time that a caster should touch water is when you cast or fire it in. Others will store them under water as you say

I know several anglers keep their casters in airtight containers and only get out enough to keep them going for half an hour or so at a time to stop them heading towards the turn.

Then again, for carp, Roy Marlow reckons they are just as good, if not better, if you have left them to go bad in the bag.

It doesn’t matter if they are wet or dry. The main point is that you need variability in the colour of your casters ie some darker ones, some medium ones and some lighter ones. This means that they sink at different rates, making it harder for fish to spot the one with the hook in it.

Fish red maggot on the hook (or worm head) as these are more resilient.

On the rear occasion I splash out on caster to fish shallow (!)I keep mine in water but stick a hand full on my side tray to darken which I use on the hook.

I feed caster and fish maggot on the hook this way you can miss a couple of bites without having to waste time re baiting ~think ~think

ive caught my fair share of fish shallow on the caster especially before pellet was about! its still a great bait now! what i do is use old bait, they smells a bit which the carp love. i buy old bait from tackle shops which you can normally get at the right price. i wash in clean water and skimm off any floaters i then dry them in a towel the best i can. i bag them in pint bags and use a pint at a time not adding water to them as they are more accurate to catapult when dry! remember the smell only puts anglers off not carp!

I put my dry casters in a largish container as soon as i get to my peg,they soon crisp up nicely when exposed to fresh air ! , then just cover them in some water to stop them turning and drying out. The key to fishing caster shallow is feeding the peg properly. Noise is key ! ~clap

I agree also that the head of a worm or a maggot or two are more resilient hookbaits but later on in the session, a single caster can be deadly.

Personally it depends on the time of year for me, when its cooler I’ll leave them dry as they turn slowly anyway, surprising how well caster shallow or deep shallow i.e. half depth can be even in winter, with maggot or worm on the hook….its not a summer only tactic IMHO!
In summer normally its in water as too expensive to waste, but to be honest its all pellet nowadays in summer, so I don’t bother with the cost or hassle until it cools down!

Oh, nearly forgot …..

Get the fish (carp or silvers) competing and you cant go wrong ~clap