It's quite easy to drink too much. 2 gallons is a **** load although many people on here will disagree with me, you should be getting plenty of water in the food that you eat. gallon a day will do. there was some article on how water bottles are turning into our pasifiers and what not, try and google that, you'll find some good info. Too much water can kill your kidneys though to not go into detail. OCCfan will probably disagree with something, we usually dont see eye to eye
Kidney damage from over consumption of water is usually completely off (as your kidneys can process something like 10 gallons of water a day. So as long as you are taking in your h20 over the course of the day no ill effects on your kidneys.)
As far as over consumption of water messing people up, like stated above it has to do with electrolyte balances (mainly sodium). Majority of us loose water and electrolytes when were sweating from busting our asses in the gym and so on (as well as just some bodily functions and then it being excreted through urine). Replacing the fluid loss is great, but when you don't replace the electolytes is when you will run into problems (not going to really dive in deep on that but electrolyte balance {especially sodium} is crucial for cell integrity, cell function, and maintenance of other electrolyte balances like potassium.)
Don't be afraid of drinking water, and in all honesty a lot of people on here could be considered "dehydrated." So drink up but at the same time replenish what your loosing along with those bodily fluids.
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Oh and disagreeing is just discussing different viewpoints and correcting each other from time to time. The whole point of AM lol