Agreed. Amphetamines will make you thirsty as hell. Couple this with AAS, creatine, extremely high protein levels, you should be drinking 1 gallon+ per day.
No, it won't cause muscle loss.
I've been using them for ADHD for years. My appetite is completely normal. Only the first few days of taking Vyvanse/Adderall did I actually notice a decrease in appetite, but it levels out.