An idiomatic way to say a task is pointless is to say it’s like carrying coals to Newcastle – Newcastle, in the north east of England, used to be a major coal mining area.
In French the equivalent is porter de l’eau à la rivière (to carry water to the river).
In German they say Eulen nach Athen bringen/tragen (to take/bring owls to Athens).
In Welsh there are quite a few equivalent expressions:
– cario glo i Fflint = to carry coal to Flint (a former coal mining area)
– cario dŵr dros afon = to carry water across a river
– bwrw heli yn y môr = to throw salt in the sea
– iro blonegen = to grease fat
– iro hwch â bloneg = to grease a sow with fat
– gwerthu mêl i berchen gwenyn = to sell honey to a bee keeper
– mynd i ‘ngheg i chwilio am fy nhafod = to go to my mouth and look for my tongue
– gyrru halen i’r Heledd = to send salt to a salt pit
– golchi traed alarch = to wash a swan’s feet
– taflu ‘fale i’r berllan = to throw apples into an orchard
What about in other languages?
In Polish, at least in the area where my family is from, we would say:
” przelewać z pustego w próżne” = to pour from one empty container into another
or
“czerpać wodę sitem” = to draw water (as from the river or well) with a strainer.
The closest Russian expression in this pattern is, of course, “ездить в Тулу со своим самоваром” (to go to Tula with your own samovar). There is also an older, but less frequent today, “в лес дрова возить” (to carry firewood to the forest).
“An idiomatic way to say a task is pointless is to say it’s like carrying coals to Newcastle.”
It’s meaning is a bit more specific than just saying a task is pointless, I think. It means bringing some kind of commodity, service etc., to a place or situation where it is not needed.
Other English expressions:
“Shutting the barn door after the horse has bolted.”
(Acting as if to prevent something from happening when it has already happened.)
“It’s no use crying over spilt milk”
(Getting upset about a mistake that has been made will not correct the situation.)
“Owls to Athens” probably is traceable to Greece. H.N. Turteltaub wrote a novel by that title set in the late 4th century BCE, in which the expression was noted in reference to a character who wanted to ship olive oil to Athens, a noted center of olive production at that time.