Basic hydration requirements

The human body requires a minimum intake of water in order to be able to sustain life before mild and then severe dehydration occurs. Adverse health effects have been noted from both mild and severe dehydration and the latter can be fatal.

The US National Institutes of Health (NIS) provides a definition of dehydration as:

  • Mild dehydration: loss of 3-5% of body weight due to fluid loss
  • Moderate dehydration: 6-10% loss of body weight
    • Signs of mild to moderate dehydration:
      • Thirst
      • Dry or sticky mouth
      • Not urinating much
      • Darker yellow urine
      • Dry, cool skin
      • Headache
      • Muscle cramps
    • Mild & moderate dehydration can be reversed by increased fluid intake and this may be enhanced through the use of salt replacement solutions.
  • Severe dehydration: (which is a medical emergency) 9-15% loss of body weight.
    • Signs of severe dehydration:
      • Not urinating, or very dark yellow or amber-colored urine
      • Dry, shriveled skin
      • Irritability or confusion
      • Dizziness or lightheadedness
      • Rapid heartbeat
      • Breathing rapidly
      • Sunken eyes
      • Listlessness
      • Shock (lack of blood flow through the body)
      • Unconsciousness or delirium
    • Severe dehydration will require rehydration strategies involving more than simple fluid replacement, and often food or other osmolar intake is needed; the process may take up to 24 hours.
  • A loss of fluids equaling 20% of a person’s body weight is fatal

Exams and Tests to detect dehydration

Your health care provider will look for these signs of dehydration:

  • Low blood pressure
  • Blood pressure that drops when you stand up after lying down
  • White finger tips that do not return to a pink color after your doctor presses the fingertip
  • Skin that is not as elastic as normal. When your health care provider pinches it into a fold, it may slowly sag back into place. Normally, skin springs back right away.
  • Rapid heart rate

How much water do you need in an emergency?

In their review, White et al. (1972) suggested that 2.6 litres of water per day is lost through respiratory loss, insensible perspiration, urination and defecation. In addition, a significant quantity of water is lost through sensible perspiration if hard work is performed. These figures led them to suggest that a daily minimum of water required in tropical climates would be around 3 litres per person.

Kleiner (1999) suggests that, based on US National Research Council guidelines in relation to hydration needs resulting from average energy expenditure and environmental exposure in the USA, the average male should consume a minimum 2.9 litres per day and the average female 2.2 litres. Approximately one-third of this fluid was considered likely to be derived from food.

As rehydration primarily relates to the replacement of lost fluid from natural processes, it is important to consider the losses of fluid from different age groups when considering vulnerable sub-populations. The losses of water from the bodies of small children are proportionally considerably greater than for adults, 15% of fluid per day as opposed to 4%. These proportionately higher losses explain why a 7 kg child requires 1 litre per day fluid to replace lost fluid compared to 2.9 litres for a 70kg adult male, the increase in replacement fluid being a factor of three compared to a 10-fold difference in weight (Kleiner, 1999). Lowbirth-weight infants need proportionally even greater fluid replacement per kilogram of weight than do other infants (Roy and Sinclair, 1975).

Pregnant women also require additional fluid replacement to ensure that foetal needs are met, as well as providing for expanding extra-cellular space and amniotic fluid. The US National6 Research Council suggests an allowance of an extra 30ml per day during pregnancy (Food and Nutrition Board, 1989). Lactating women have additional water requirements, leading to an additional requirement of 750ml to 1 litre per day for the first six months of lactation (Food and Nutrition Board, 1989).

The elderly may not require additional volumes of water, but may be at greater risk from dehydration due to decreasing thirst sensations (Phillips et al., 1984). Furthermore, studies have noted a relationship between age and the ability of the body to concentrate urine, suggesting an increasing water requirement to maintain good renal functioning (Rowe et al., 1976).

For the terminally ill, Jackonen (1997) highlights a range of benefits and burdens related to dehydration, with benefits accrued from lower levels of distress and lower awareness of pain and reduced requirements for urination with the pain and discomfort that this may cause. Benefits of hydration include preventing dehydration and malnourishment as well as prolonging life and avoiding health problems such as renal failure. The benefits and burdens associated with dehydration amongst the terminally ill often relate to medical hydration (intravenous, nasogastric or nutrition administration) and therefore will have little impact on volumes of water required in a general domestic supply.

In developing countries, White et al. (1972) and Gleick (1996) suggest that a minimum of 3 litres per capita per day is required for adults in most situations. However, households with least access to water supplies are more likely to be engaged in at least moderate activity and often in above-average temperatures. Data from the US Army reported in White et al. (1972) provides estimates of water quantity needs at different temperatures and activity levels. This indicates that at 25oC with moderate activity in the sun (for instance agricultural work) approximately 4.5 litres are required to maintain hydration. This rises to about 6 litres at 30oC or when hard work in the sun is undertaken at 25oC. Although the US Army has more recent recommendations for hourly intake of water per hour in relation to heat categories and activity intensity to prevent heat injury, this do not easily translate into non-military activity. They do, however, stipulate that hourly fluid intake should not exceed 1.08 quarts (1.03 litres) and that daily intake should not exceed 12 quarts (11.35 litres) (United States Army Center for Health Promotion and Preventive Medicine, 2003).

Overdrinking of water

The SPHERE project is a collaboration of a wide range of NGOs and humanitarian agencies that has produced guidelines on the minimum standards for provisions for refugees. It recommends 2-4 gallons/day (7.5-15 litres/day) as the basic water needed per person per day in emergencies. In some situations, only water used for drinking and preparing food needs to be treated, which still amounts to 1.5-2.5 gallons/day (5.5-9 litres/day). In refugee situations, the UNHCR calculates 5.25 gallons per person per day (20 litres/person/day) for domestic needs and personal hygiene. The absolute minimum amount of water required for survival is 1.8 gallons/day (7 litres).

Survival needs: water intake (drinking and food) 2.5 – 3 litres per day Depends on the climate and individual physiology Basic hygiene practices 2 – 6 litres per day Depends on social and cultural norms Basic cooking needs 3 – 6 litres per day Depends on food type and social and cultural norms Total basic water needs 7.5 – 15 litres per day

Water Treatment for Drinking

Chemical Treatment

If water is polluted with dirt or sediment, strain it into a container through paper towels, paper coffee filters, or several layers of clean cloth to remove any sediment or floating matter.

Disinfect the strained water with liquid household chlorine bleach (chlorine) OR with tincture of iodine. Household bleach consists of chlorine (Cl2) gas dissolved in an alkali-solution, such as sodium hydroxide (NaOH). Chlorine reacts with sodium hydroxide to form sodium hypochlorite (NaOCl).

NOTE: DO NOT use the granular form of household bleach, it is POISONOUS!

To disinfect water, use the following formula: Amount of chlorine bleach to add: Amount of tincture of iodine 2% to add: Amount of water Clear water Cloudy water Clear water Cloudy water 1 quart 2 drops 4 drops 3 drops 6 drops 1 gallon 8 drops 16 drops 12 drops 24 drops 5 gallons ½ teaspoon 1 teaspoon ¾ teaspoon 1½ teaspoons NOTE: If liquid chlorine bleach is older than one year, the amount used should be doubled, as it loses strength over time. Purchase an eye dropper to add bleach or iodine to the water. Use the eye dropper for this purpose ONLY. Mix well by stirring or shaking the water in a container. Let stand for 30 minutes before using. A slight chlorine odor should be detectable in the water. If not, repeat the dosage and let stand for an additional 15 minutes before using. If the water can be boiled, the Centers for Disease Control and Prevention recommend that it be boiled for at least 1 minute. This should remove any harmful bacterial contamination. Check with your local Health Department for local recommendations. Water purification tablets are available in drug stores and sporting goods stores and are recommended for your first aid kit. Follow the directions on the package to purify water. Water purification tablets have a shelf life of 2 years and lose their effectiveness if they get damp before use. Purify only enough water at one time to last for 48 hours. This will minimize the chances of re-contamination.

Calculate the number of gallons of water in a box-type container:

Volume (gallons) = 7.5 x L x W x H

L = length in feet W = width in feet H = height in feet

Example: If a water container is 6 feet long, 3 feet wide and 2 feet high, then the volume is 7.5 x 6 x 3 x 2 or 270 gallons. Therefore, use 3 tablespoons of liquid chlorine bleach for disinfection.

Calculate the number of gallons of water in a cylindrical container:

Volume (gallons) = 6 x D2 x H

D = diameter in feet H = height in feet

Example: If a water container is 4 feet in diameter and 5 feet high, then the volume is 6 x 42 x 5 which is the same as 6 x 16 x 5 or 480 gallons. Therefore, 5 tablespoons of liquid chlorine bleach should be used for disinfection.

How does chlorine disinfection work?

Chlorine kills pathogens such as bacteria and viruses by breaking the chemical bonds in their molecules. Disinfectants that are used for this purpose consist of chlorine compounds which can exchange atoms with other compounds, such as enzymes in bacteria and other cells. When enzymes come in contact with chlorine, one or more of the hydrogen atoms in the molecule are replaced by chlorine. This causes the entire molecule to change shape or fall apart. When enzymes do not function properly, a cell or bacterium will die.

When chlorine is added to water, underchloric acids (HOCL) form:

  • Cl2 + H2O -> HOCl + H+ + Cl*

Depending on the pH value, underchloric acid partly expires to hypochlorite ions (OCl):

  • Cl2 + 2H2O -> HOCl + H3O + Cl
    HOCl + H2O -> H3O+ + OCl*

This falls apart to chlorine and oxygen atoms:

  • OCl -> Cl + O*

Underchloric acid (HOCl, which is electrically neutral) and hypochlorite ions (OCl, electrically negative) will form free chlorine when bound together. This results in disinfection. Both substances have very distinctive behaviour. Underchloric acid is more reactive and is a stronger disinfectant than hypochlorite. Underchloric acid is split into hydrochloric acid (HCl) and atomair oxygen (O). The oxygen atom is a powerful disinfectant. The disinfecting properties of chlorine in water are based on the oxidizing power of the free oxygen atoms and on chlorine substitution reactions.

The cell wall of pathogenic microorganisms is negatively charged by nature. As such, it can be penetrated by the neutral underchloric acid, rather than by the negatively charged hypochlorite ion. Underchloric acid can penetrate slime layers, cell walls and protective layers of microorganisms and effectively kills pathogens as a result. The microorganisms will either die or suffer from reproductive failure.

The effectivity of disinfection is determined by the pH of the water. Disinfection with chlorine will take place optimally when the pH is between 5.5 and 7.5. Underchloric acid (HOCl) reacts faster than hypochlorite ions (OCl); it is 80-100% more effective. The level of underchloric acid will decrease when the pH value is higher. With a pH value of 6 the level of underchloric acid is 80%, where as the concentration of hypochlorite ions is 20%. When the pH value is 8, this is the other way around. When the pH value is 7.5, concentrations of underchloric acid and hypochlorite ions are equally high.

Which factors determine the effectivity of chlorine disinfection?

Factors which determine chlorine disinfection effectivity: Chlorine concentrations, contact time, temperature, pH, number and types of microorganisms, concentrations of organic matter in the water.

E. coli 0157 H7 bacterium < 1 minute
Hepatitis A virus about 16 minutes
Giardia parasite about 45 minutes
Cryptosporidium about 9600 minutes (6,7 days)

Disinfection time for several different types of pathogenic microorganisms with chlorinated water, containing a chlorine concentration of 1 mg/L (1 ppm) when pH = 7.5 and T = 25 °C

Read more:

How UV Disinfection Works Unlike chemical approaches to water disinfection, UV provides rapid, effective inactivation of microorganisms through a physical process. When bacteria, viruses and protozoa are exposed to the germicidal wavelengths of UV light, they are rendered incapable of reproducing and infecting. UV light has demonstrated efficacy against pathogenic organisms, including those responsible for cholera, polio, typhoid, hepatitis and other bacterial, viral and parasitic diseases. In addition, UV light (either alone or in conjunction with hydrogen peroxide) can destroy chemical contaminants such as pesticides, industrial solvents, and pharmaceuticals through a process called UV-oxidation. UV light damages the DNA and RNA of microorganisms and prevent them from infecting Microorganisms are inactivated by UV light as a result of damage to nucleic acids. The high energy associated with short wavelength UV energy, primarily at 254 nm, is absorbed by cellular RNA and DNA. This absorption of UV energy forms new bonds between adjacent nucleotides, creating double bonds or dimers. Dimerization of adjacent molecules, particularly thymine, is the most common photochemical damage. Formation of numerous thymine dimers in the DNA of bacteria and viruses prevents replication and inability to infect.

Effectiveness of UV A significant body of scientific research has proven UV light’s ability to inactivate an extensive list of pathogenic bacteria, viruses and protozoa. UV offers a key advantage over chlorine-based disinfection, due to its ability to inactivate protozoa that threaten public health – most notably Cryptosporidium and Giardia. The release of these harmful microorganisms into receiving lakes and rivers by wastewater facilities utilizing chlorine disinfection increases the potential of contamination in communities that rely on these same bodies of water for their drinking water source and recreational use. Drinking water treatment plants can benefit by using UV since it can easily inactivate chlorine-resistant pathogens (protozoa), while reducing chlorine usage and by-product formation.


SODIS is the process of using the sun’s energy to disinfect water. Sunlight has two components that make this happen: ultraviolet and infrared radiation. These two types of radiation work together in synergy to kill up to 99.9% of microorganisms.

SODIS Process

  • Choose colorless, transparent PET water or soda pop bottles with few surface scratches for use.

    • PET bottles are marked with “recyclable #1”. Most 2 liter coke bottles are PET bottles, so these are very common

    PET Label

    • containers cannot be more than 4 inches thick. Standard 2 liter or smaller soda bottles are fine.
    • Containers must be clear; not colored, and not opaque. Colored bottles absorbs UV-A light.
    • At least 2 bottles for each member of the family should be exposed to the sun while 2 other bottles are ready for consumption, so each family member requires 4 plastic bottles for SODIS.
    • Check the water tightness of the bottles, including the condition of the screw cap.
    • Remove labels and wash the bottles before first use.
      • You can sterilize bottles by placing them closed, empty in the sun for six hours or by washing them thoroughly (and triple-rinsing with agitation) with sterile water.
    • PET breaks down in the sun, so you eventually have to replace the container.
    • Replace cloudy, scratched, or leaky containers.
    • Do not use PVC containers except as a last resort. PVC leaches chemicals into the water, especially when placed in the sun.
  • Water from contaminated sources is filled into the bottles.

    • To improve oxygen saturation, bottles can be filled three-quarters, shaken for 20 seconds (with the cap on), then filled completely and recapped.
    • Very cloudy water with a turbidity higher than 30 NTU must be filtered prior to exposure to the sunlight.

      • Water Turbidity
      • Test of water turbidity: if you place bottle with water on a newspaper, can you read a headline through it (from neck to bottom)? Turbidity test
      • To decide whether the water needs filtering, place the filled bottle on the SODIS Logo (see Figure below) on top of a table in the shade (to avoid light interference) and look through the bottle from top to bottom. If you can read the letters through the water, water turbidity is less than 30 NTU. If you can still see the sun rays of the Logo, turbidity is less than 20 NTU. If water turbidity is higher than 30 NTU, coarse and settleable solids can be separated by storing the raw water for one day, and turbidity can be reduced possibly by flocculation / sedimentation (using alum sulphate or crushed Moringa oleifera seeds) or by filtration.

  • Filled bottles are then exposed to the Sun.

    • Bottles will heat faster and to higher temperatures if they are placed on a sloped Sun-facing corrugated metal roof as compared to thatched roofs.
    • The bottles must be laid horizontally in the sun, not vertically. This increases the area exposed to the sunlight and reduces the depth of the water the light must penetrate. (With turbidity of 26 NTU, only half of the UV-A radiation penetrates farther than 10cm)
    • Ideally, you should place the bottles in a hot place; on a roof, on a sheet of corrugated metal, or on asphalt or dark rocks. If these are not available, at least try to shield the bottles from cooling breeze, but don’t shade them.
  • The treated water can be consumed directly from the bottle or poured into clean drinking cups.
    • The risk of re-contamination is minimized if the water is stored in the bottles.
Suggested treatment schedule
Weather conditions Minimum treatment duration
Sunny (less than 50% cloud cover) 6 hours
Cloudy (50–100% cloudy, little to no rain) 2 days
Continuous rainfall Unsatisfactory performance;
use rainwater harvesting

A total solar radiation intensity of at least 500 W/m2 is required for approximately 6 hours for SODIS to be effective.The most favorable regions for this is located between latitude 15°N and 35°N, and also 15°S and 35°S. These regions have high levels of solar radiation, with limited cloud cover and rainfall, and with over 90% of sunlight reaching the earth’s surface as direct radiation. The second most favorable region lies between latitudes 15°N and 15°S. these regions have high levels of scattered radiation, with about 2500 hours of sunshine annually, due to high humidity and frequent cloud cover.

USA Insolation Map

Drawbacks of SODIS

  • It does not remove chemical contaminants.
  • It does not improve the taste of the water.

For Geeks: How does SODIS work?

Three effects of solar radiation are believed to contribute to the inactivation of pathogenic organisms:

  • UV-A interferes directly with the metabolism and destroys cell structures of bacteria.
  • UV-A (wavelength 320–400 nm) reacts with oxygen dissolved in the water and produces highly reactive forms of oxygen (oxygen free radicals and hydrogen peroxides) that are believed to also damage pathogens.
  • Cumulative solar energy (including the infrared radiation component) heats the water. If the water temperatures rises above 50 °C (122 °F), the disinfection process is three times faster.

    • In fact, water does not have to be boiled to kill microorganisms. Heating the water to an elevated temperature over a long period of time (50-60°C for one hour) has the same effect as boiling.
    • At a water temperature of about 30 °C (86 °F), a threshold solar irradiance of at least 500 W/m2 (all spectral light) is required for about 5 hours for SODIS to be efficient. This dose contains energy of 555 Wh/m2 in the range of UV-A and violet light, 350–450 nm, (This is about 6 hours of mid-latitude (European) midday summer sunshine).
    • At water temperatures higher than 45 °C (113 °F), synergistic effects of UV radiation and temperature further enhance the disinfection efficiency.

The figure above shows scanning electron micrograph of oocysts of C. parvum. (a) Healthy C. parvum. (b) C. parvum after heating to 40◦C for 10 h. (c) C. parvum after heating to 40 ◦C and applying sunlight (870W/m2) for 10h. (source)

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