THis is a modern day myth, there is no proven benefit of stuffing your stomach with water.
Not true
Not true, xcan cause muscle soreness but not joint. By the way a healthy person with access to water, drinking as he wishes never gets dehydrated.
Allah has given us a beautiful system in the body, which increases your urge to drink whenever your body needs it.
Absolutely.
Dehydration along with mineral loss (mostly potassium) causes muscle soreness.