How do you keep a plaster cast dry for showering?

DD has a full arm plaster cast. I put a bag on it and secured it, but water still got in.
Any hints on best way to keep It water tight?

With ds, I wrapped it in cling wrap after the plastic bag, but he ended up deciding on a bath anyway.

We prob will bath but she needed to wash her hair. I will wrap in cling wrap fir next bath.

You can actually buy proper cast covers for showers etc! Google it.

can you just wash it in the laundry tub?

cling wrap over the cast & a bit further up the arm, tape the ends where the glad wrap meets the skin
then grab a garbage bag (not a shopping bag unless it is one of those thick bags like from a clothing shop), get some tape and tape it in two or three places (at the edge of the cast, a bit further up & then where the plastic meets the skin).

This should cope with a hair-washing shower.

We got away with cling wrap and tape. If you stretch it a bit so it grabs and go around 3 or 4 layers then it stays on fine.

i ended up bathing DD and taking her to the hairdresses twice a week for them to wash her hair for her but she was 7 years old so it was a bit easier
if they have to change the cast at any time, ask them for a fibreglass cast instead- can get a little wet and soo much lighter and tougher@!!!
and of course you can then request colours lol
hugs hun

Apparently she is too young for fiberglass

Thanks everyone for advice. I have also cut up an old rainbow knee high sock and using it as a cover during the day. We are in day 2 and it is already filthy!