how to kill a baby houseplant

my houseplant, Dhaun is dying.
we are having yellowing, wilted leaves, spots, scorched stalks, the works.
leaves count are down 13% since last week.
i was literally going insane trying to figure out what am i doing wrong.
and Dhaun is supposed to be the no-fuss-leave-it-alone-it'll-just-grow kinda plant.
how hard is it to keep a house plant from dying?
what kind of incompetent idiot would kill a house plant?
i was hoping to prove (to myself) that should i succeed in rearing Dhaun (bountiful green glossy leaves, creeping thick vines) i would upgrade to keeping a pet, maybe a fish.
at this rate the fish would die before you could say 'stanley'.

am thinking it might be the tap water im giving it, so i switched to watering Dhaun with mineral water.
(RM5.30 evian water in fact. shut up)
cant say its working, Dhaun's still shedding leaves.
thinking that maybe it was not getting enough sunlight, eventhough the labels says Dhaun only needs half sunlight.
so now, every morning i would leave Dhaun at the window sill, hoping it would catch some second hand sunshine (what sunshine is after the people in better room locations are done with it)
but Dhaun still persists in dying.

but last night, after snipping away another load of wilted, mutated leaves from Dhaun's anorexic, scrawny body, i wondered if Dhaun is perhaps suicidal.
i wouldnt blame it, i know i wouldnt want to be a houseplant under my care. but as deranged as i am to buy imported water and talk to a potted plant, i am not deranged enough to think a plant would have any common concious sense. yet.
im killing my houseplant and i dont know how.
then, accidently my sleeve snagged the end of the table and almost tipped over Dhaun's funky orange pot.
it didnt fell but the sloshing sound it made me wonder.
in the orange clay pot, under the plastic underwear pot, apparently theres urm, some excess water. by 'some' i mean there's enough water to flood Ghobi desert.
ive been tad overzealous in watering my plant that the roots are dying from water rot.
ahem. dying slowly being pickled in the swampy soil. ugh.
death by evian.
wow.

im still getting a fish soon though. because theres no way i'd overwater a fish.
unless i find some other moronic way to eff that up.
cause of death: excessive caring. overly loved to death.
snort. thats just great.