Just to give you a helping with some basic Welsh:
Dwr = Water
Ych-y-fi = Yuck/horrible
Crappio = I'm sure you can work this one out
A farmer was out on his Welsh hillside tending his flock one day, when he saw a man drinking with a cupped hand from the stream which ran down from one of his fields.
Realising the danger, the farmer shouted over to the man "paid a yfed yr dwr! Mae'n ych-y-fi!"
The man at the stream lifted his head and put a cupped hand to his ear, shrugged his shoulders at the farmer, and carried on drinking.
Realising the man at the stream couldn't hear him, the farmer moved closer.
"Paid fachgen! Dwr ych-y-fi! Sheep crappio yn y dwr!"
Still the walker couldn't hear the farmer. Finally the farmer walked right up to the man at the stream and once again said "Dwr yn ych-y-fi! Dim drinkio!".
"I'm dreadfully sorry my good man, I couldn't understand a word you said dear boy!" said the man at the stream in a fine English accent.
"Oh I see" said the farmer, "I was just saying, if you use both hands you can get more in..."