Maintaining water balance is essential for your survival.

For this reason, your body has a sophisticated system for regulating when and how much you drink.

When your total water content goes below a certain level, thirst kicks in.

This is controlled by mechanisms similar to breathing — you don’t need to consciously think about it.

For the majority of people, there probably isn’t any need to worry about water intake. The thirst instinct is very reliable 

There really is no science behind the 8×8 rule. It is completely arbitrary 

That said, certain circumstances may call for increased water intake.

The most important one may be during times of increased sweating. This includes exercise and hot weather, especially in a dry climate.

If you’re sweating a lot, make sure to replenish the lost fluid with water. Athletes doing very long, intense exercises may also need to replenish electrolytes along with water.

Your water need also increases during breastfeeding, as well as several disease states like vomiting and diarrhea.

Furthermore, older people may need to consciously watch their water intake because the thirst mechanisms can start to malfunction in old age 

SUMMARY

Most people don’t need to consciously think about their water intake, as the thirst mechanism in the brain is very effective. However, certain circumstances do call for increased attention to water intake.