Water makes up about 60% of the human body weight. 67% of ATC (total body water) is made up of intracellular fluid (IBC) and 33% of extracellular fluid (ECL)
The water content of the body must be kept constant. Variations of no more than 7% of the ATC are tolerated. Our body has a mechanism that controls the body’s water balance.
The thirst center is located in the hypothalamus, which detects water loss through osmoctors and volumoctors. In case of dehydration, the hypothalamus directly controls antidiuretic hormone ( ADH) and indirectly aldosterone to induce the kidney to reabsorb water.
Water intake comes from food, drink, and metabolism. Water is absorbed in the small and large intestines. In the adult, a recommended intake of 1 mL of water per kilocalorie consumed is recommended.
Water losses occur through urine, feces, perspiratio insensibilis and sweating. Extrarenal losses are obligatory. The kidney performs osmoregulatory function.
Water is a regulator of velvet volume, body temperature. It allows the transport of nutrients, digestive processes and the removal of waste.
Food water must be drinkable.
It is drinkable if it has these characteristics:
- contains no more than 1500mg/L of mineral salts
- is not chemically contaminated
- is palatable
Mineral salts are:
- Calcium salts: 20 200 mg/L. The amount of calcium is important in case of a diet poor in this element.
- sodium salts: up to 20 mg/L that is less than 10% of the daily sodium supply;
- chlorine salts: about 42 mg/die against a requirement of 2000mg/die
- potassium salts about 2 mg/L, not significant amount
Water hardness is the content of calcium carbonate per liter of water.
Mineral waters are classified according to their dry or fixed residue, that is the amount of salts after the evaporation of 1 L of water at 180 °C. They can be oligomineral, mineral, rich in mineral salts in relation to the dry residue per mg/L.
Waters with sulfates greater than 200 mg/L may be considered mildly laxative, and may be useful in combating cholesterol.
Waters with chloride above 200 mg/L have the effect of balancing the biliary tract, intestines and liver.
Waters with magnesium over 50 mg/L promote purgative action; bicarbonate over 600 mg/L promote digestive processes and are recommended for hepatobiliary disorders.
Waters with fluorides greater than 1 mg/L are recommended to prevent tooth decay and in pregnancy
Waters with more than 200 mg/L are to be avoided in case of hypertension
Waters with iron above 1 mg/L are recommended in case of anemia but to be avoided in case of gastroduodenitis.
WATER FAO REPORT
The rate at which human water use increased during the 20th century was twice the rate of population growth.
In most regions of the world, evaporation from irrigated agricultural land accounts for by far the largest share of human water use.
On average, 3000 liters of water are needed to produce the daily food needs of a human being.
Expected population growth coupled with dietary changes suggest that 60% more food will be needed by the year 2050, rising to 100% in developing countries.
Irrigated agriculture represents 20% of total cultivated land but contributes to 40% of total food production.
Non-irrigated agriculture accounts for 80% of total cultivated land and contributes 60% of total food production, making it the primary source of agricultural production globally. Drought alone is the most common cause of food shortages in developing countries.
An estimated 40 percent of the world’s population lives in water-scarce regions.
Each year, 30 percent of all food produced globally – 1.3 billion tons – is lost.