Baby has diarrhoea.?

Hi there. For a couple of days our 7 month baby son has had diarrhoea. This has come after a course of antibiotics to sort out a 'cold' (or more properly a bacterial infection causing lots of mucus). We were told to expect a little diarrhoea but this has now lasted a few days after the antibiotics have finished. We rang NHS direct who said he had a gastric bug and they suggested 24hrs on cool boiled water only which should kill off the bug. The problem is that our son does not like taking water from a bottle or any kind of cup. I have just this minute come from a screaming baby. I am worried that he will not get any fluid intake. Any speedy suggestion would be very welcome indeed. Thank you.