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Regarding Nitrates in a borehole WHO Guidelines for Drinking Water state that for emergencies (p108):
6.2.5 Chemical and radiological guidelines Many chemicals in drinking-water are of concern only after extended periods of exposure. Thus, to reduce the risk of outbreaks of waterborne and water-washed (e.g. trachoma, scabies, skin infections) disease, it is preferable to supply water in an emergency, even if it significantly exceeds the guideline values for some chemical parameters, rather than restrict access to water, provided the water can be treated to kill pathogens and can be supplied rapidly to the affected population. Where water sources are likely to be used for long periods, chemical and radiological contaminants of more long-term health concern should be given greater attention. In some situations, this may entail adding treatment processes or seeking alternative sources. Local actions that can be considered in the event of a short-term guideline exceedance or emergency are discussed in section 8.6.
Nitrates and nitrites do have a short term risk though for bottle fed babies:
Specifically the WHO Guidelines factsheet for nitrates and nitrites (p417) states that:
Guideline value for nitrate 50 mg/litre to protect against methaemoglobinaemia in bottle-fed infants (short-term exposure ) Guideline value for nitrites 3 mg/litre for methaemoglobinaemia in infants (short-term exposure)
(Provisional guideline value for nitrite 0.2 mg/litre (provisional) (long-term exposure) The guideline value for chronic effects of nitrite is considered provisional owing to uncertainty surrounding the susceptibility of humans compared with animals.)
Guideline value for combined nitrate plus nitrite The sum of the ratios of the concentrations of each to its guideline value should not exceed 1.
Guideline derived from:
Nitrate (bottle-fed infants): in epidemiological studies, methaemoglobinaemia was not reported in infants in areas where drinking-water consistently contained less than 50 mg of nitrate per litre
Nitrite (bottle-fed infants): application of body weight of 5 kg for an infant and drinking-water consumption of 0.75 litre to lowest level of toxic dose range, 0.4 mg/kg of body weight
The main issue is nitrites reacting with haemoglobin in red blood cells to block oxygen transfer, causing blue baby syndrome. Nitrates are reduced to nitrites by bacteria, which is why the nitrate guideline is there. High stomach pH (more likely in bottle-fed babies) and gastrointestinal infections increase this bacterial reduction of nitrates to nitrites. Using high nitrate water for bottle fed babies (the water being the major part of their fluid intake), especially with gastro-intestinal infections exacerbates this problem.
These figures are primarily based on the effect of nitrites and nitrates on bottlefed babies. Mothers of bottlefed infants and expectant mothers should be the target of any intervention. If they can be properly identified and measures put in place for them then the issue is less of an emergency concern.
It is worth checking the nitrite values as well as nitrates and ensuring that ratios of nitrites and nitrate tested values are less than the minimum.
Where possible use other water sources, with large piped water supplies it is possible to blend the high nitrate water with lower nitrate water.
At a household level ensure that the water supply is microbiologically safe - this reduces the likelihood of gastrointerestinal infections. Target mothers with young infants (especially bottle fed) and expectant mothers in terms of health messages, water quality safety and the consequences of high nitrate water, provide other microbiologically safe water (bottled water?) for bottle feeding.
Taken from WHO Guidelines on Drinking Water Quality 3rd Edition (p417 - 419)
Significant bacterial reduction of nitrate to nitrite does not normally take place in the stomach, except in individuals with low gastric acidity or with gastrointestinal infections. These can include individuals using antacids, particularly those that block acid secretion, and potentially bottle-fed infants (due to relatively higher stomach pH), although there is some uncertainty regarding the latter. In humans, methaemoglobinaemia forms as a consequence of the reaction of nitrite with haemoglobin in the red blood cells to form methaemoglobin, which binds oxygen tightly and does not release it, so blocking oxygen transport. Although most absorbed nitrite is oxidized to nitrate in the blood, residual nitrite can react with haemoglobin. High levels of methaemoglobin (greater than 10%) formation can give rise to cyanosis, referred to as blue-baby syndrome. Although clinically significant methaemoglobinaemia can occur as a result of extremely high nitrate intake in adults and children, the most familiar situation is its occurrence in bottle-fed infants. This was considered to be primarily a consequence of high levels of nitrate in water, although there have been cases of methaemoglobinaemia in weaned infants associated with high nitrate intake from vegetables. Bottle-fed infants are considered to be at greater risk because the intake of water in relation to body weight is high and, in infants, the development of repair enzymes is limited. In clinical epidemiological studies of methaemoglobinaemia and subclinical increases in methaemoglobin associated with drinking-water nitrate, 97% of cases occurred at concentrations in excess of 44.3 mg/litre, with clinical symptoms associated with the higher concentrations. The affected individuals were almost exclusively under 3 months of age.
While drinking-water nitrate may be an important risk factor for bottle-fed infants, there is good evidence that the risk of methaemoglobinaemia is primarily increased in the presence of simultaneous gastrointestinal infections, which increase endogenous nitrate formation, may increase nitrate reduction to nitrite and may also increase the intake of water in combating dehydration. Cases have been described in which gastrointestinal infection seems to have been the primary cause of methaemoglobinaemia.
Most cases of methaemoglobinaemia reported in the literature are associated with contaminated private wells that also have a high probability of microbial contamination and predominantly when the drinking-water is anaerobic, which should not occur if it is properly disinfected.
The guideline value for nitrate of 50 mg/litre as nitrate is based on epidemiological evidence for methaemoglobinaemia in infants, which results from short-term exposure and is protective for bottle-fed infants and, consequently, other parts of the population. This outcome is complicated by the presence of microbial contamination and subsequent gastrointestinal infection, which can increase the risk for this group significantly. Authorities should therefore be all the more vigilant that water to be used for bottle-fed infants is microbiologically safe when nitrate is present at concentrations near the guideline value However, the water must also be known to be microbiologically safe. The latter is a minor modification of previous guidance to give greater emphasis to the role of microbiological quality.
The most appropriate means of controlling nitrate concentrations, particularly in groundwater, is the prevention of contamination (Schmoll et al., 2006). This may take the form of appropriate management of agricultural practices, the careful siting of pit latrines and septic tanks, sewer leakage control, as well as management of fertilizer and manure application and storage of animal manures. It may also take the form of denitrification of wastewater effluents.
Methaemoglobinaemia has most frequently been associated with private wells. It is particularly important to ensure that septic tanks and pit latrines are not sited near a well or where a well is to be dug and to ensure that animal manure is kept at a sufficient distance to ensure that runoff cannot enter the well or the ground near the well. It is particularly important that the household use of manures and fertilizers on small plots near wells should be managed with care to avoid potential contamination. The well should be sufficiently protected to prevent runoff from entering the well. Where there are elevated concentrations of nitrate or where inspection of the well indicated that there are sources of nitrate close by that could be causing contamination, particularly where there are also indications that microbiological quality might also be poor, a number of actions can be taken.Water should be boiled or disinfected by an appropriate means before consumption.Where alternative supplies are available for bottle-fed infants, these can be used, taking care to ensure that they are microbiologically safe. Steps should then be taken to protect the well and ensure that sources of both nitrate and microbial contamination are removed from the vicinity of the well.
In areas where household wells are common, health authorities may wish to take a number of steps to ensure that nitrate contamination is not or does not become a problem. Such steps could include targeting mothers, particularly expectant mothers, with appropriate information about water safety, assisting with visual inspection of wells to determine whether a problem may exist, providing testing facilities where a problem is suspected, providing guidance on disinfecting water or where nitrate levels are particularly high, providing bottled water from safe sources or providing advice as to where such water can be obtained.
With regard to piped supplies, where nitrate is present, the first potential approach to treatment of drinking-water supplies, if source substitution is not feasible, is to dilute the contaminated water with a low-nitrate source. Where blending is not feasible, a number of treatment techniques are available for drinking-water. The first is disinfection, which may serve to oxidize nitrite to the less toxic nitrate as well as minimize the pathogenic and non-pathogenic reducing bacterial population in the water. Nitrate removal methods include ion exchange (normally for groundwaters) and biological denitrification (normally for surface waters). However, there are disadvantages associated with both approaches, including the need for regeneration and disposal of spent regenerant with ion exchange, the complexities of operation and the potential for microbial and carbon feed contamination of the final water with biological dentrification.
Care should be taken with the use of chloramination for providing a residual disinfectant in the distribution system. It is important to manage this to minimize nitrite formation, either in the main distribution system or in the distribution systems of buildings where chloramines are used to control Legionella.