Women collect water from a roadside municipality tap at Sagalipara, on the outskirts of Guwahati. Picture by UB Photos
Sustainable solutions to drinking water contamination, such as rainwater harvesting, are urgently needed
Hundreds of villages on the southern bank of the Brahmaputra in central Assam are affected today by fluoride contamination of water sources. The problem is so serious that apart from the Assam Valley, the rainforest belt of Karbi Anglong and regions in neighbouring states such as Nagaon district have now been included in the “fluoride map” of the country.
Karbi Anglong is by far the worst affected, with approximately 10 per cent of its population suffering from dental or skeletal fluorosis. Fluoride is a general protoplasmic poison, known to cause major functional derangement such as enzyme inhibition, cardiovascular collapse and specific organ damage, which may result in critical biochemical defects. A colourless and odourless natural pollutant, fluoride comes into contact with groundwater from its source of origin in mineral rocks. The concentration of fluoride in groundwater basically depends on extended contact of the water with fluoride-bearing minerals.
Geologically, Karbi Anglong and parts of Nagaon district have numerous joints, fractures and faults. These have been found to have areas with large quantities of sedimentary rocks and unconsolidated materials, all of which are known for their high fluoride content.
After West Bengal and the bordering districts of Bangladesh, arsenic in groundwater was detected in several parts of Assam, Arunachal Pradesh, Manipur, Nagaland and Tripura. This was evidenced by a study conducted by different agencies. Apart from those in the Northeast, millions more drink arsenic-tainted water from wells in India.
Water with arsenic content can be ingested for years before severe symptoms show up. Researchers say such symptoms are now appearing in people who drink water from tubewells in a number of countries.
Serious health problems are posed by ingestion of arsenic through drinking water. While some palliative treatment of patients of arsenicosis is possible, it is clear that the first step in treating patients, and preventing others from falling sick, is to identify safe sources of water for drinking and cooking in arsenic-affected areas.
In areas where drinking water contains unsafe levels of arsenic, the immediate concern is finding a safe source of drinking water. There are two main options: finding a new safe source and removing arsenic from the contaminated source. In either case, the drinking water supplied must be free of harmful levels of arsenic, but also from bacteriological contamination and other chemical contaminants.
Various strategies are being worked out for fluoride mitigation, including identifying surface sources and drawing water from them, providing de-fluoridation units at habitation levels as well as household levels, de-silting tanks and recharging ground water to dilute fluoride levels in the aquifer.
To prevent a fluorosis disaster, it is imperative that safe water supply is made available, with more emphasis on surface water sources, as they are generally free from fluoride contamination.
Researchers have been constantly trying to devise a simple, foolproof and cost-effective filter but the devices invented have failed in one way or another, either in terms of cost, weight or efficiency. Some scientists propose that we should entirely skirt the problem of arsenic filtration by returning to surface water. Drinking from shallower surface wells that do not reach down into arsenic-tainted aquifers is another way of addressing the problem.
Coagulation and filtration are among the most common arsenic removal technologies. By adding a coagulant such as alum, ferric chloride or ferric sulphate to contaminated water, much of the arsenic can be removed. Membrane methods for arsenic removal include reverse osmosis and nano-filtration. These make use of synthetic membranes, which allow water through but reject larger molecules, including arsenic, chloride, sulphate, nitrate and heavy metals.
Membranes that are currently available are more expensive than other options of arsenic removal. However, membrane technology is advancing rapidly and it is conceivable that future generations of membranes could be used effectively in rural settings.
Rainwater harvesting is potentially an effective and cheap method of storing clean drinking water. Rainwater is the primary source for all water and is one of the purest forms of water, without any groundwater contaminants. Harvesting rainwater appropriately for the Northeast and using it for drinking and cooking would ensure clean potable arsenic, fluoride and iron-free water for consumption.
Harvesting of rainwater simply involves collection of water from surfaces on which rain falls and subsequently storing this water for later use. Normally, water is collected from the roofs of buildings and stored in rainwater tanks.
The process of rooftop rainwater harvesting would mean keeping the roof clean, collecting the water through gutters or pipes, filtering the water to remove silt and other sediments and storing the water for later use. Except for thatched roofs, all other roofs, such as country tiles, RCC, asbestos and corrugated iron sheet roofs, are ideal for collection. After two stages of filtration, the clear water is stored in a closed container. Water free of organic contaminants, if kept away from air and sunlight, can be stored for a long time without it getting polluted.
The key to selecting an appropriate technology is to involve community members in all stages of the process, from technology selection to operation and maintenance. In this way, a sense of ownership can be generated and an appropriate, sustainable technology selected. To allow water users to make their own informed choices, information about a wide range of options should be provided to them.
Until water users understand the problem of arsenic contamination and its impact on their health and have reliable information about safe alternatives, they will be unwilling and unable to make an informed choice for changing their water use patterns. The biggest challenges ahead lie in applying viable technologies in poor, rural settings, and in enabling those communities to choose safe sources of water for drinking and cooking.
A hazardous pollutant is the last thing that we would like in our drinking water. After an aquifer has been contaminated, it is difficult to entirely isolate a contaminant and becomes extremely costly to remove it. Even after the source of contamination has been removed, an aquifer may remain contaminated for anywhere from a few years to a few centuries. Thus, it is often not realistic to talk about a cure for groundwater contamination. Prevention is the key to this malady, and prevention includes finding the major sources of contamination and learning to control them.
When the contaminants are identified, the immediate priority must be to find a safe alternative source of drinking and cooking water for the affected communities. Alternate sources must be not only pollutant-free, but also microbiologically safe.
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