Although there are better choices, condoms are a small, light weight way to carry water, especially if protected by being carried in a bandanna or such.
In a survival situation it is great to find water when you need it, but if you can't take some with you for later then you have lost a huge opportunity.
I suggest one gallon freezer bags or the replacement plastic bags for drinking bladders.
2l “Platypus” bottles take up essentially no space empty, and are much stronger than a condom.
FWIW