Hi welcome to Health care magic forum,
Water like fullness in ear associated with post nasal drip
and cough indicate upper and lower respiratory tract
infection with eustachian tube catarrah with serous ottits media .
In my opinion you avoid taking cold water and keep your self protected and take rest with plenty of water.
You can take a broad spectrum antibiotic and a antihistamines with a nasivion
nasal drop 2 drops 3 times for 2 to 3 days .
If no relief then you must see an ENT specialist
for proper evaluation.