I Have The 5th Metatarsal Bone Fracture About A Month

i have the 5th metatarsal bone fracture about a month ago and my orthopedic surgeon has put me on walkable plaster. today while taking shower a little amount of water went inside the cast and i tried to dry it using absorbent tissue. can we make use of the same cast once again and just change the cotton or we need to change the whole cast. it is quite expensive (came up to around 5000 INR and just got it done a week back)