Fluid balance

The core principle of fluid balance is that the amount of water lost from the body must equal the amount of water taken in; for example, in humans, the output (via respiration, perspiration, urination, defecation, and expectoration) must equal the input (via eating and drinking, or by parenteral intake).

Water-electrolyte imbalance produces headache and fatigue if mild; illness if moderate, and sometimes even death if severe.

Water treatment also adds some minerals, such as calcium, zinc, manganese, phosphate, fluoride, and sodium compounds.

Other elements, such as fluoride, while beneficial in low concentrations, can cause dental and other problems at high levels.

)[citation needed] Oral rehydration therapy (ORT), is type of fluid replacement used as a treatment for dehydration.

[citation needed] If blood pressure is low (hypotension), the filtration rate in the kidneys will lessen, causing less fluid reabsorption and thus less urine output.

[citation needed] An accurate measure of fluid balance is therefore an important diagnostic tool, and allows for prompt intervention to correct the imbalance.

[11] A constant supply is needed to replenish the fluids lost through normal physiological activities, such as respiration, sweating and urination.

[citation needed] The human kidneys will normally adjust to varying levels of water intake.

Thus, there will be an increase in the secretion of antidiuretic hormone, causing fluid to be retained by the kidneys and urine output to be reduced.

The activated renin–angiotensin system stimulates the zona glomerulosa of the adrenal cortex which in turn secretes the hormone aldosterone.