My Son-in-law Complains Of Dark Urine Even Though He Drinks

my son-in-law complains of dark urine even though he drinks lots of water even 2 or 3 bottles during the night without needing to urinate often. He does sweat heavily at night and his lower back aches. He has heavy nose bleeds a couple of times a week. He also is under a lots of stress at work which causes him to feel tight in his chest. He won't go see a doctor so if I can tell him what it might indicate he may consider it. Thank you so much.