I know, that there is the standard 8x8oz glasses or ~ 3 liters of water per day. But today I read, that since about 75% of muscle is water, people using their muscles intensively need more water, about two times as much as standard.
So my question is: at which point does more become too much?
How much water can I drink before I start hurting my kidneys?
Background: I'm currently drinking about 5 liters of water per day if training, about 4 if on rest.
The kidneys of a healthy person can process about 15 liters of water a day - well beyond your current intake. The only caveat is that you can't drink it all at once! If you space your water consumption over a long enough time then it's very difficult to induce water intoxication.
If you were to drink your normal 5 liters in the span of an hour, say, you will start to get hyponatremia which is the dilution of salt in the body. When that happens you will start to see symptoms similar to being drunk - confusion, lack of balance, etc. If that occurs it's a serious medical condition that could result in your death.
I drink about a gallon or more of water a day and have been doing so for several years. The amount isn't as important as how long it takes you.
"Normal, healthy (physically, nutritionally and mentally) individuals have little reason to worry about accidentally consuming too much water. Nearly all deaths related to water intoxication in normal individuals have resulted either from water drinking contests, in which individuals attempt to consume large amounts of water, or long bouts of intensive exercise during which electrolytes are not properly replenished, yet excessive amounts of fluid are still consumed.[1] Water can be considered a poison when over-consumed just like any other substance[citation needed]. The recommendation from the medical field is to drink at least 1 to 2 liters per day[2] depending upon body mass. Water intoxication would only occur at levels far higher than that."
Source: Wikipedia
The original research that stated we need about 8 glasses of water per day included all sources. This includes water from food as well as all fluids we drink. There has never been any reputable research that show we need to drink 8 glasses of water per day in addition to other sources.
Following a water contamination disaster in Walkerton, Ontario, Canada it was found that excessive water intake appears to damage the kidneys and blood vessels.
I try to ensure I drink enough that my skin remains flexible, and I need to empty
The Walkerton, Ontario investigation as noted by BillThor determined that people drinking 4+ liters of water per day experienced proteinuria (i.e. kidney damage):
"Canadian doctors are warning that drinking too much water may cause loss of kidney function... Researchers... identified 100 otherwise healthy adults who had a condition called proteinuria, or abnormal amounts of protein in their urine. ... Proteinuria can cause kidney failure and is a sign of microvascular disease, where the heart's tiny arteries are damaged, causing cardiac disease and cardiac death. ... They were drinking, on average, at least four litres of fluid per day. ... Some people were drinking six litres. One woman, a health care worker, was drinking eight."
http://www.canada.com/topics/bodyandhealth/story.html?id=612070ac-ae0a-47c5-b4a1-39e1b1ce9735
And here's a scholarly paper about it: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2175005/
In other words, humans cannot safely drink 15 liters per day.
This information does not appear to be widely known, since google search results are dominated by (1) the old weakly supported 8x8 advice and (2) that the only possible danger from water is water intoxication by rapid ingestion of large quantities (http://en.wikipedia.org/wiki/Water_intoxication).
There's no need to over drink water. And everyone has different water needs so there is no limit.
Fortunately you have something called a brain that will tell you when your not thirsty anymore! Drinking excessively past this limit can be bad for your health. Your brain is good at regulating your thirst, listen to it!
I would concentrate on rest, eating and your workout program if you want to build muscle mass.
