There are key organs and system that assist in ensuring the body maintains homeostasis in the case of water-salt balance.
The excretory system: When one sweats, a lot of water content of the blood can drop (this is what causes the individual to be thirsty). In order to maintain a certain water-salt balance, the excretory system passes some salt out of the body in the form of urine (this is the reason the urine is usually yellowish but small in volume during the summer).
Endocrine system: When water content of the blood drops, vasopressin (also called antidiuretic hormone) is released into the bloodstream stimulating the kidneys to conserve water and release less urine (as said earlier). However, if the body is hydrated, less vasopressin is released and more water is passed in the urine.
In order to balance out the equation, you bed to double the amount of H atoms you have and the number of CL atoms. to do this you put a 2 infrount of the HCL
