Someone at running club had told me about water posioning a few months back. Apparently, once you go too far you still feel thirsty and it's a bit like being high on Ecstacy and you can just overload your organs. After the embryo transfer I had to measure liquid in and out... yeah I know, don't think about it too much and one day I'd had 3 litres of liquid in and got told off by the nurse for drinking too much. She said aim for around 2 litres of liquid (water, tea, juice, etc.) per day. The 8 glasses of water thing is ok, if that's all you drink, otherwise you should drop your water intake accordingly.