~ CHAPTER 2 ~ IRRIGATION BASICS ~
Edition 5 of July, 2007 (Updated October 2010 and January 2011)

~ TABLE OF CONTENTS ~

(2-A) ~ Irrigated Land Salinity Basics ~ [A1]~General, [A2]~Degradation mechanisms, [A3]~Quantifying Salinity, [A4]~Salt Tolerance of Crops, [A5]~Salt Levels in Soils, [A6]~Drainage Ponds, ~

(2-B) ~ Aridity ~ [B1]~Global, [B2]~Latin America, [B3]~Africa,

(2-C) ~ Irrigation Technology ~ [C1]~Groundwater Use, [C2]~Central-Pivot Irrigation, [C3]~Drip Irrigation, [C4]~Hydroponics, [C5]~Miscellaneous, [C6]~Surge Techniques, ~

(2-D) ~ Irrigated Land Productivity ~

(2-E) ~ Irrigation-Related Diseases ~ [E1]~General, [E2]~Drinking Salty Water, [E3]~Schistosomiasis, [E4]~Groundwater Nitrates, [E5]~Miscellaneous, ~
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ir2

NOTE: The notation (su4) means that the adjacent data was used in the document analyzing the sustainability of the productivity of the world's systems for producing food, fiber and water.

SECTION (2-A) ~Irrigated Land Salinity Basics ~ [A1]~General, [A2]~Degradation mechanisms, [A3]~Quantifying Salinity, [A4]~Salt Tolerance of Crops, [A5]~Salt Levels in Soils, [A6]~Drainage Ponds, ~

Part [A1] ~ Salinity Basics ~ General ~

Two types of soil salinization can be distinguished: Primary salinization is a natural process caused by movement of saline water in the soil originating from saline springs, saline seepage or groundwater upward fluxes (capillary movement), driven by climatic dryness, or due to coastal influence in surrounding lands. Secondary salinization, on the other hand, is caused by improper human activities, such as excessive or inadequate irrigation and the lack of proper drainage (00E1).

Salt buildup (salinization) is seen as one of the gravest threats to irrigated agriculture and to global food security (99P1).

The principal effect of salinity is to reduce the availability of water to the plant by high osmotic concentration of salts in the soil solution (71R1).

An excellent discussion of salinity in irrigation systems is in Ref. (81P1).

Part [A2] ~ Salinity Basics ~ Degradation Mechanisms ~

The major effects of salinity on soil properties are swelling of clay soils, dispersion of fine soil particles, crust formation, and a decrease in water movement within the soil profile. The amount of sodium adsorbed to the soil particles and the amount of sodium in the irrigation water greatly influences the degree to which salinity affects soil properties. Options for the management of salinization are determined by the salinity or sodicity of the soil and the water. The major determinant for reclamation of salt-affected soils is the presence and functioning of proper drainage systems, which are critical for adequate leaching of accumulated salts (00E1).

Particularly in low-lying river valleys, as irrigation raises the level of the water table near the surface of the land, some of the water evaporates, leaving salt behind, resulting in salinization which makes the land toxic to crops (99P1).

Once underground water with a salt content of 0.1% (1000 ppm) (quite acceptable to crops) is within several feet of the surface, capillary evaporation residues raise the salt content of the top 3 ft. of soil to the intolerable level of 1% in 2 decades (76E1).

The traditional method of dealing with salinization due to rising water tables is alternate-year fallowing. Details of the system are discussed in Ref. (77G1). Comments: As population pressures on the land grow larger, the alternative of alternate year fallowing become increasingly difficult to justify from a near-term perspective.

Waterlogging starves plant roots of oxygen and inhibits their growth (90P1).

Waterlogging (a process which destroys irrigation systems) is described on p. 115 of Ref. (76E1).

Physical mechanisms by which irrigation systems collapse are described in Ref. (70P4).

With poor drainage, salts accumulate in the water table. Excessive irrigation, rain or floods raise the water table. With a further capillary rise when soil is wet, dissolved salts and exchangeable Na. are bought into the root zone, or even to the soil surface (58J1).

Irrigation water sometimes contains sodium. So as water evaporates and transpires, Ca. and Mg. precipitate as carbonates, leaving Na+ dominant in the soil solution. Unless it is washed down in the water table, Na+ tends to be adsorbed by colloidal clay particles, deflocculating them and leaving the resultant structureless soil almost impervious to water (58J1).

Part [A3] ~ Salinity Basics ~ Quantifying Salinity ~

Even the best water supplies typically have salt concentrations of 200-500 ppm (90P1).

The upper limit (US EPA) for drinking water is 500 mg./liter of total dissolved solids (Ref. 20 of (85E1)).

Salinity of water rises by 300-400 p.p.m. while passing once through the urban circuit. Salinity is not reduced by any of the usual sewage treatment processes (77A2).

US Salinity Laboratory classification of the salinity hazard to crops of irrigated water (81S3):
Low ~ |100 250 ppm. | Medium ~ |250-750 ppm.
High~ |750-2250 ppm.| Very High| ~2250+ ppm. (81S3).

Agricultural damage begins when salt contents of irrigation water reaches 700-850 mg./liter, depending on soil condition and crop type (Ref. 20 of (85E1)).

Salt content of the Colorado River flowing into Mexico: 800 ppm. in 1960, 1500 ppm. in 1962 (81S3).

Ocean water averages about 35,000 ppm. (3.5%) dissolved solids (carbonates, chlorides and sulfates of calcium, magnesium and sodium) (81P1) (77M1).

Because of its high salt content (35,000 ppm), 2% of seawater mixed with freshwater makes the water unusable for either drinking or irrigation (00S1).

Part [A4] ~ Salinity Basics ~ Salt Tolerances of Crops ~

Salt tolerances of various crops are plotted as relative yield vs. average soil salinity in Fig. 4 of Ref. (77S2).

Soil salinities (in ppm) needed to reduce crop yields by 50% relative to normal yield (77S2)
citrus~ |1200 |wheat~ ~ ~ ~ |4300 ppm
lettuce |1600 |safflower~ ~ |4300
melons~ |1600 |cotton ~ ~ ~ |4900
alfalfa |2500 |barley ~ ~ ~ |5500
sorghum |3700 |Bermuda grass|5600

Salt tolerances of various crops (71R1)
High Salt Tolerance (18-10 mmhos/ cm.)
- -Barley, cotton, sugar beets, rape, safflower
- -garden beets, asparagus, spinach
- -date palm
- -alkali sacaton, salt grass, bermuda grass, Rhodes grass, Canada wild rye, western wheat grass, Birdsfoot trefoil
Medium Salt Tolerance (10-4 mmhos/ cm.)
- -rye, corn, wheat, sunflower, oats, castor beans, rice, sorghum
- -tomato, potatoes, broccoli, carrots, cabbage, onion, bell pepper, peas, lettuce, squash, sweet corn, cucumber
- -pomegranate, figs, olives, grapes
- -white clover, alfalfa, yellow clover, reed canary, perennial ryegrass, Dallis Grass, sour clover, Sudan grass, oat hay, tall fescue, wheat hay, meadow fescue, orchard grass
Low Salt Tolerance (4-2 mmhos/ cm.)
- -field beans
- -radishes, celery, green beans
- -pears, almonds, apples, peaches, oranges, strawberries, grapefruit, lemons, prunes, avocadoes
- -white dutch clover, alsike clover, red clover, Ladino clover

Note: One mmho/ cm. is approximately equivalent to 700 ppm. of total soluble salt (400 ppm. for MgCl; 1000 ppm. for sodium bicarbonate). Water having a conductivity of one mmho/ cm. would contain approximately 1900 pounds of salts per acre-ft. of water (71R1). Above tolerances are based on a 50% yield reduction.

Most crops under irrigation will tolerate dissolved salts under 600 mg./ liter. If drainage and leaching are adequate, irrigation will work with water with 500-1500 mg./liter of dissolved salts. Between 1000 and 2000 mg/liter (ppm.), irrigation must be frequent to avoid leaching. Water with 3000-5000 mg/ liter produces only crops that are highly tolerant of salts (77S1), (77M1).

A new salt-resistant plants can thrive even when salt levels are twice the amount that would kill a normal crop of corn. Arabidopsis thaliana, a member of the Mustard family, includes broccoli and cauliflower (99U2).

Suwanee Bermuda Grass can tolerate 12,000 mg/ liter of salt (77M1).

At soil salinity of 4 millimhos/ cm., field beans yield 40% of their potential; carrots 60%, and neither produces a crop at 8 millimhos/cm. At medium soil salinity (16 millimhos/ cm.) dates and cotton yield 57% of their potential (85G1). Comments: To convert between millimhos/ cm. and mg/liter see Section (8-A) or (8-B) above.

Part [A5] ~ Salinity Basics ~ Salt Levels in Soils ~

Salt-affected Soils of the World (in units of 1000 km2) (88S1)
North America ~ ~ | 158| N. and Cent. Asia |2117
Mexico/Cent. Amer.| ~20| Southeast Asia~ ~ | 200
South America ~ ~ |1292| Australasia ~ ~ ~ |3573
Africa~ ~ ~ ~ ~ ~ | 805| Europe~ ~ ~ ~ ~ ~ | 508
South Asia~ ~ ~ ~ | 876| Total ~ ~ ~ ~ ~ ~ |9548

A map showing the global distribution of salt-affected soils is shown on page 7 of (88S1). A breakdown by country is on page 9-10.

Part [A6] ~ Drainage Ponds ~

Drainage ponds offer only a short-term solution to the long-term problem of collecting salty water from irrigated land. Eventually the salt crust builds up and the ponds become useless (99P1).

In California's San Joaquin Valley, drainage pond areas total 10-15% of the irrigated land being drained (50% when drainage systems capture a fair amount of salty groundwater) (99P1).

In Australia's Murray River Basin, 3% of the irrigated land must be dedicated to drainage ponds (for the salty water from the drainage pipes) (99P1).

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SECTION (2-B) - Aridity ~ [B1]~
Global, [B2]~Latin America, [B3]~Africa,

See a listing of large databases in Chapter 8 Section (8-E) for sources of tabulations of:
~ average precipitation during 1961-1990 (mm/ year), by country
~ average precipitation during 1961-1990 (km3/ year), by country
~ total renewable water sources (km3/ year), by country
~ total groundwater produced internally (km3/ year), by country
~ total surface water produced internally (km3/ year), by country
~ overlap in surface and groundwater (km3/ year), by country

A "Desertification Map of the World" (78D1) classifies the world's lands as "slightly", "moderately", "severely", or "very severely" desertified.

Comparison of Runoff to precipitation (log-log plot in (58L1))
Precip.(in./year)~|7.8 |10.0|15. |20.| 30.| 40.| 50.| 60.
Runoff (in./ year)|0.1 |0.29|1.0 |2.7| 7.2| 15.| 25.| 35.
Runoff (cm./ year)|0.25|0.74|2.54|6.9|18.3|38.1|63.5|88.9

(The difference is presumably lost through evaporation.)

Part [B1] ~ Aridity ~ Global ~

Desert Facts and Useful Links
(See http://ag.arizona.edu/OALS/IALC/desertfacts.htm ) (Visited 8/11/06)

~ Arid Lands Maps ~ (http://ag.arizona.edu/OALS/IALC/About/aridlands_map.html)

About one-third of the earth's land area is either arid or semiarid - in total size, this is roughly equal to the combined areas of North and South America (http://ag.arizona.edu/OALS/IALC/About/aridlands_map.html). Comments: Does "earth's land area" mean all land or just ice-free land?

Drylands are found in over 60 of the world's nations. 30 nations, many in the Middle East and Africa, are at least 75% drylands (http://ag.arizona.edu/OALS/IALC/About/aridlands_map.html).

The world's largest area of drylands is the Saharan-Arabian-Iranian-Thar Desert, which stretches 6000 miles from North Africa through the Middle East to northwest India (http://ag.arizona.edu/OALS/IALC/About/aridlands_map.html).

Dry lands occur in the tropics and the mid-latitudes. Tropical dry lands occur from 15-35 degrees latitude and extend from west coasts into continental interiors. Mid-latitude dry lands occur from 35-55 degrees latitude and are concentrated in continental interiors (http://ag.arizona.edu/OALS/IALC/About/aridlands_map.html).

Because deserts are too dry for many wood-decaying fungi to exist, termites play a crucial ecological role by eating, breaking down, and recycling cellulose (wood, grasses, cactus skeletons, and dung). Without termites, the entire desert ecosystem would collapse (http://ag.arizona.edu/OALS/IALC/About/aridlands_map.html).

Cities now house almost half of the world's population, and mega-cities with more than 10 million population are increasing. (per AAAS Atlas of Population and Environment, http://atlas.aaas.org/ ). Roughly 800-900 million people in the world's dry lands live in cities. (Philip Dobie, 2001, UNDP: Poverty and the Drylands).

Deserts: geology and resources by A. S. Walker, a USGS online book, 1998 (http://pubs.usgs.gov/gip/deserts/contents/).
Deserts in the American Southwest by DesertUSA (http://www.desertsusa.com/life.html)
Some Like it Hot Bureau of Land Management Environmental Education Resources (http://www.blm.gov/education/00_resources/articles/some_like_it_hot/index.html/)
Related Websites  (http://ag.arizona.edu/OALS/IALC/links/1stlevel.html)

Maps of Africa, Asia, Australia, North America, and South America showing the location of extremely arid, arid, and semi-arid regions are found in Ref. (70D1). These maps can be measured planimetrically to produce the results shown in the table below. (All areas are in units of million km2, and include only ice-free land.) Precipitation rates on semi-arid land, arid land, and hyper-arid land can be converted to run-offs (water available for irrigation) using the Langbein-Schumm relationship (58L1) - or see above). The results are shown in Columns 6-9 in the table below. (Runoffs are in units of km3/ year.).

- - - - - | ~ ~ ~ ~ ~ Areas~ ~ ~ ~ ~ | ~ ~ ~ ~ Runoffs
Region- - | Total| Semi | Arid| Hyper|Total|Semi |Arid|Hyper
- - - - - | Land | Arid | ~ ~ |-Arid | ~ ~ | Arid| ~ ~|-Arid
Australia | ~7.62| 2.52 | 3.66| 0.00 |101.8| 88.7|13.1| 0.0
Africa~ ~ | 29.64| 6.37 | 7.23| 4.50 |250.6|224.2|25.8| 0.6
Cent.Amer.| ~2.79| 0.61 | 0.64| 0.03 | 23.8| 21.5| 2.3| 0.0
S. America| 17.54| 1.74 | 1.20| 0.21 | 65.5| 61.2| 4.3| 0.0
US.(48) ~ | ~7.68| 1.87 | 0.83| 0.04 | 68.8| 65.8| 3.0| 0.0
Canada~ ~ | ~9.22| 0.40 | 0.00| 0.00 | 14.1| 14.1| 0.0| 0.0
Eurasia ~ | 53.79| 8.58 | 8.62| 1.08 |332.9|302.0|30.8| 0.1
Oceania*# | ~0.27| 0??? | 0?? | 0??? | ~0? | ~0? | 0? | 0.0
Alaska~ ~ | ~1.53| 0??? | 0?? | 0??? | ~0? | ~0? | 0? | 0.0
Totals ***|130.07|22.09 |22.18| 5.86 |857.5|777.5|79.3| 0.7
PRECIP.(cm./ year) (average of the range) 37.5|17.5 <5.0
Runoff (cm./ year)(from precip.and Ref.(58L1) 3.52|0.358 <0.013

Total (hyper-arid +arid +semi-arid) = 50.13 million km2
*# excluding Australia // *** Columns may not add due to round-off.
Comments: The total run-off from lands where irrigation is commonly practiced (858 km3/ year) should be compared to total water-use for irrigation (3500 km3/ year). Clearly the bulk of irrigation water must come from land receiving over 50 cm/ year of precipitation - or depleting ground water. The runoff from the world's ice-free lands is about 40,000 km3/ year, though only 14,000 of this amount represents a reliable supply.
Comments: Arid lands receive 10-25 cm. of rainfall annually (85D1). Semi-arid land receives 25-50 cm. of rainfall annually (85D1).

Part [B2] ~ Aridity ~ Latin America ~

[B2a] ~ Aridity ~ Latin America ~ Mexico ~

About 85% of Mexico's land area is either arid or semi-arid (97R1). (la)

Part [B3] ~ Aridity ~ Africa ~

Drylands, including hyper-arid deserts, comprise 19.59 million km2 or 65% of the African continent, and one-third of the world's drylands. One-third of this area is hyper-arid deserts (6.72 million km2). These are uninhabited, except in oases. The remaining two-thirds, or 12.87 million km2, comprise the arid- and semi-arid lands (97D1). (la)

The human population in Africa's arid- and semi-arid lands has doubled in the past 3 decades to nearly 400 million, and continues to expand at 3%/ year (97D1).

The climate of the region from Algeria to Peoples Republic of Yemen has been the same for at least the past 3000 years (77A1).

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SECTION (2-C) ~ Irrigation Technology ~ [C1]~Groundwater Use, [C2]~Central-Pivot Irrigation, [C3]~Drip Irrigation, [C4]~Hydroponics, [C5]~Miscellaneous, [C6]~Surge Techniques, ~

Part [C1] ~ Groundwater Use ~

Farmers began tapping ground water on a large scale after 1950, as powerful diesel and electric pumps became available (p. 255 of (99P1)).

Part [C2] ~ Irrigation Technology ~ Central-Pivot Irrigation ~

C.P.I. is used on 6 million acres (24,000 km2) in the US. Each system covers 132 acres in a 160-acre square. Cost: $50,000/ system. The electrical cost is $1500-$2500/ year (same as for a sprinkler system) for 160 acres. Labor cost: $1.40/ acre/ year (compared with $4.00/ acre/ year for a sprinkler network). C.P.I. uses 40% less water than ditching does - and it can be used in rolling terrain (76O1). (This is repeated in Section (7-A).)

Part [C3] ~ Irrigation Technology ~ Drip irrigation ~

Many Indian farmers are switching to drip irrigation, but mainly for high value crops such as fruits and vegetables (06M2).

(Water is delivered by porous or perforated pipe installed on or below the soil surface.)

Drip irrigation technology is described in Ref. (77S1). Its efficiency, water-usage, and relation to salinity are also described. Drip irrigation can be used on hilly land, e.g. sugar cane in Hawaii, or on slopes of 20-30%, or avocado orchards on slopes of 50-60% (77S1).

Using drip irrigation does not entail salt accumulation in the root zone (93P2).

Switching from furrow- or sprinkler irrigation to drip systems cuts water use by 30-60% (96P1).

Israel pioneered the use of highly efficient drip irrigation; Israeli farmers cut average water use on each irrigated hectare by a third, even while raising crop yields. Global use of drip irrigation has grown 28-fold since the mid-1970s, but still accounts for less than 1% of world irrigated area (97P3). Comments: Irrigation water is heavily government-subsidized virtually worldwide. This works against increased use of drip irrigation.

Drip-irrigated sugar cane yields 12-30% more per unit-area, while cutting water use by 30-65% (p. 177 of (99P1)).

Israel uses drip-irrigation on more than 50% of its irrigated land (Ref. 37 of (96G1)).

Part [C4] ~ Irrigation Technology ~ Hydroponics ~

Information of general interest on the technology of hydroponically grown vegetables (lettuce) in New York is found in Ref. (84M1).

Part [C5] ~ Irrigation Technology ~ Miscellaneous ~

With techniques available today, farmers could cut their water demands by 10-50%, industries by 40-90%, and cities by a third with no sacrifice of economic output or quality of life (97P3).

Part [C6] ~ Irrigation Technology ~ Surge Techniques ~

In the Texas High Plains, supplied by the dwindling Ogallala aquifer, many farmers have adapted old-fashioned furrow irrigation systems to a new "surge" technique that distributes water more uniformly and reduces waste. Water savings have averaged 25%, and the initial investment of about $3000/ km2 is typically recouped within the first year (97P3).

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SECTION (2-D) ~ Irrigated Land Productivity ~

The extent of irrigated area per person reached a high of 47 ha. per 1000 people in 1978 and has been shrinking steadily since 1992. In 2003, per-capita irrigated area dropped below 44 ha. per 1000 people, the lowest level of the past four decades. With population growth outpacing growth in irrigated area, this figure is unlikely to rebound substantially (06M1).

Some 36% of all the world's food comes from artificially irrigated land. Both India and China, among other countries, rely on irrigation for more than half of their domestic food production.


(
S. Postel, (1997). Last Oasis: Facing Water Scarcity. W. W. Norton & Company, London, p. 49.) Comments: Other figures give 60% of the world's food comes from irrigated land (in dollar terms, not tonnage terms). In tonnage terms, other data gives 40%.

Water stress at the flowering stage of maize, for example, will reduce yields by 60%, even if water is adequate during the rest of the crop season (04M1).

The 2.71 million km2 of irrigated cropland (00F1) produces 40% (weight basis) of the world's crops ((97W1), p. 9). Comments: That percentage is about 60% on a dollar-value basis - See below.

Irrigation contributes about one-third of global crop production, yielding about 2.5 times as much per unit area as non-irrigated land (Ref. 52 of (94K1)).

Irrigation generally results in a 4-5-fold increase in productivity over dry-farming (74M2).

Some 33% of the 1985 harvest (world-wide) came from the 17% of the world's croplands that are irrigated (85P1).

The 17% of all cropland under irrigation produce one-third of the world's total food supply (98H1).

Irrigation on 14% of the world's croplands produces 25% or more of the world's crops (70T1).

Irrigation of 15% of the world's farmlands produces 40% of its output (87P2).

A non-referenced UN statement claims 18% of the world's cultivated land is irrigated, and produces 50% of the world's food ().

About 1/3 of the global harvest comes from the 16% of the world's croplands that are artificially watered (94P2).

Dregne and Chou (Ref. 18 of (97C1)) estimate the value of production of irrigated cropland at $625/ ha/ year (as compared to $95/ ha/ year for rain-fed cropland, and $17.50/ ha/ year for rangelands).

Irrigated lands account for 16% of the world's croplands, but 40% of the world's food (Ref. 4 of (96P1)). Comments: This implies that irrigated croplands are 3.6 times more productive per unit area than non-irrigated croplands.

Irrigation was the source of more than 50% of the increase in global food production during 1965-1985 (Ref. 28 of (96G2)).

More than 60% of the value of Asian food crops comes from irrigated land (98H1).

The product value of irrigation water in Israel is $0.18/ m3 (76E2).

Israel's irrigation system can feed 1000 people/ km2 - compared to a global average of 250/ km2 (77A2).

SECTION (2-E) ~ Irrigation-Related Diseases ~ [E1]~General, [E2]~Drinking Salty Water, [E3]~Schistosomiasis, [E4]~Groundwater Nitrates, [E5]~Miscellaneous, ~

Part [E1] ~ Irrigation-Related Diseases ~ General ~

Diseases associated with irrigation are discussed in Ref. (77C1).

Part [E2] ~ Irrigation-Related Diseases ~ Drinking Salty Water ~

Little has been done about the ecological devastation of the Aral Sea on the border of Kazakhstan and Uzbekistan, according to the UNESCO Courier. Soviet-era irrigation projects diverted the rivers that feed the Aral Sea, causing it to shrink. Drinking water contains four times more salt per liter than that recommended by the World Health Organization, resulting in increases in kidney diseases, diarrhea and other ailments. The region has some of the world's highest rates of infant mortality and child deformities. Tuberculosis has reached "epidemic proportions" (UNESCO Courier (1/27/00)).

Part [E3] ~ Irrigation-Related Diseases ~ Schistosomiasis ~

About 200 million people in at least 71 African, Asian and Latin-American countries suffer from Schistosomiasis. This debilitating disease spreads almost as fast as irrigated agriculture expands (77C1).

Large-scale water projects were a major contributor to the 75% global increase in schistosomiasis during 1947 and the early 1980s (95G2).

Schistosomiasis, a snail-borne disease, causes 1 million deaths/ year, and is expanding its range as human activities provide suitable habitats in contaminated fresh water. Following construction in 1968 of Egypt's Aswan High Dam and associated irrigation systems, prevalence of Schistosoma mansoni organisms in humans in the region increased from 5% to 77% (98P2).

Part [E4] ~ Irrigation-Related Diseases ~ Groundwater Nitrates ~

In central Nebraska, groundwater-nitrate concentrations commonly exceed 10 mg./ liter of Nitrogen (N) (the US standard) (79A1). The nitrate standard in the EU is the same as in the US, although the EU expresses its standard in terms of Nitrate.  The conversion is 10 mg NO3-N = 44.3 mg Nitrate according to an email from Prof. Dr. K. Schaller of 01/05/11. 

Part [E5] ~ Irrigation-Related Diseases ~ Miscellaneous ~

In the Ganges River valley in India, one of the most heavily populated areas on earth, arsenic has invaded all the way to the Himalayas, an area that is home to half a billion people. People are at serious risk in 17 countries around the world - including China, Vietnam, Argentina and the US, where limits set by the World Health Organization are exceeded. In Bangladesh about 50 million people are at risk in the world's worst mass poisoning disaster. The Bangladesh government has spent only $7 million of the $32 million given by the World Bank in 1998 for clean-up. In the Indian state of Bihar, many of the 83 million people upstream of the Ganges delta use tube wells likely to contain arsenic. 80% of the population in northern India drinks water from underground sources, mostly from simple hand-pumped tube wells sunk in the past 30 years to replace polluted surface water supplies. Most tube wells have never been tested for arsenic. In one village, the untouchables, who not allowed to drink water from village tube wells, were the only fit persons. It was warned last year that 10 million people in the Terai plain of Nepal (part of upper Ganges valley), may be drinking contaminated water. Many already have symptoms of arsenic poisoning. A researcher in India, Chakraborti, says many of the half a billion people living on the Ganges plain could be at risk. Up until 20 years ago few people drank groundwater, but then aid agencies began promoting it as a safe reliable source of drinking water to replace surface water contaminated with sewage.
In Vietnam, tests show that groundwater from tube wells sunk beneath the Red river delta, home to 11 million people, including the capital Hanoi, contain arsenic levels up to 300 times the WHO safe limit
("Arsenic's Fatal Legacy Grows Worldwide", New Scientist, 8/6/03).

WHO statistics show about 90,000 annual recorded deaths linked to water-borne diseases (96M2).

It takes less than a 1% deficiency in our body's water to make us thirsty. A 5% deficit causes a slight fever. An 8% shortage causes the glands to stop producing saliva, and skin turns blue. A person cannot walk with a 10% deficiency. A 12% deficiency causes death (98S1).

About 9500 children die every day (3.47 million/ year) from lack of water or, more frequently, from diseases caused by polluted water. (UN data) (98S1). Comments: This datum seems too high.

Some 35 million of Bangladesh's 130 million people drink arsenic-tainted water in what the World Health Organization calls "largest mass poisoning of a population in history." The government, in an attempt to get people off of pond water, the breeding ground for lethal diseases, has been drilling wells. But the underground aquifers from which the wells draw water are contaminated with arsenic, which causes cancer. Due to a bureaucratic snarl, most of Bangladesh's 11 million wells have yet to be tested. The poison in small doses is slow, taking 2-10+ years to work its damage. Estimates of the number who will die from arsenic poisoning range from 1-3 million. Arsenic can be filtered from water, but this requires effort and training (02U2).

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