понос in English:

he had an attack of diarrhoea

He got diarrhoea when he had food poisoning.

I had diarrhoea last night and had to go to the toilet six times.

He has diarrhoea.

I've got a diarrhoea. I keep going to the toilet.

It is essential to drink a lot of fluids when one has diarrhoea.

After drinking contaminated water it is very likely you will suffer from diarrhoea.