Emma Watson fell ill after Darren Aronofsy banned water bottles on the set of 'Noah'.
The filmmaker wanted to encourage a ''pro-environment'' atmosphere during filming to echo the messages of the movie, which led to the ''delirious'' actress drinking ''stagnant'' water in a bid to stay hydrated in the early morning heat.
She said: ''Because of the storm, Douglas [Booth] and I ended up shooting most of our scenes between 4am and 7am - and at that time I never function well.
''Because the film has a pro-environment message, Darren didn't want anyone drinking from plastic water bottles on set either. So that made things slightly harder.
''Everything we used had to be recycled or recyclable. Having no water bottles on set at five in the morning - when you're exhausted and delirious - wasn't ideal.
''I was so tired one morning I picked up a mug from my trailer and drank some stagnant water that had been there for the duration - so three months. I was so ill.''
And the 23-year-old actress was stunned when the director told her to ''use'' her illness in the scene.
She continued to Wonderland magazine: ''I came in the next day and was like, 'Darren, I don't think I can do this, I'm really sick.' He was like, 'Use it for the scene.' And I turned round to the bus and was like, 'Is he joking? He is joking right?' and there was deadly silence.''
Filming was often tough on the movie because of extreme weather conditions, and the heat even saw Ray Winstone come close to passing out on set.
Douglas said: ''We started filming in the summer in New York. It was so hot that Ray Winstone at one point, who wore a beard and heavy make-up, nearly fell down a flight of stairs.''
Emma added: ''His make-up was literally melting off his face. Then we decided to shoot the soaking wet scenes. We literally went through all the seasons.''