this is a "water" joke !!

Bart had bought a new tank for salt-water-fish .
At home he realised he needed salted water .
So he stept in his car and drove all the way to the sea .
There he saw a fisher man and asked him for a bucket of sea-water .Okay , said the man , that will cost you one dollar !
Bart payed and returned home . There he realised he needed much more buckets of the water .
So he drove back to the sea . There the sea had withdrawn , and it was low tide ;
He joined the fisherman and said : well you lucky guy , you seem to have sold lots of buckets today hey !!!!!!!!!!!!