Global Water Jobs Blog Series: Water Issues 2: Household Water Treatment

WATER ISSUES:
Household Water Treatment

When sourced, raw water is likely to be contaminated with harmful pathogens and poisonous chemicals that can cause severe diseases (e.g. cholera, typhoid fever and hepatitis). Consequently, water needs to be treated before consumption in order to remove these pollutants.

In developed countries, water is extensively treated in large plants with several stages (coagulation and flocculation tanks, clarifiers, filtration units, disinfection basins…) to ensure its safety before being distributed through the piped system. However, in developing countries, such large-scale infrastructure does not exist, and water is treated with smaller, household systems.

These household water treatment systems have proved to be a simple and sustainable solution, improving the quality of the water consumed and reducing the risks of illness and death. Although none of these household-level treatment systems result in complete treatment when applied alone, they can be very helpful in minimizing the risk of consuming contaminated water.

Drinking water treatment methods at household level can be divided into those methods that result in the destruction of microbes (disinfection) and those that involve their removal (filtration). Coming up, we are going to review the common ways of treating water and addressing the challenges that they present according to the following criteria:



Effectiveness – It removes most disease-causing bacteria and viruses.



Quickness – It takes less than one hour to treat the water.



Applicability – It can be used in all types of water, in particular those with high turbidity.



Cost – It can be acquired at an affordable price.



Maintenance – It can be operated without important maintenance requirements.




 

DISINFECTION METHODS

Boiling

Boiling water is probably the oldest and most effective way to remove all kind of pathogens. This method consists in leaving the water in a rolling boil for 5-10 minutes, and consuming it once it has cooled. However, despite its effectiveness and simplicity, this method requires large amount of fuel, which could cause problems of availability and cost in many regions.




Chlorination

Disinfecting water with chlorination is a method that has been known for decades and is extremely effective against most bacteria, as well as some viruses. The method consists in mixing the contaminated water with chlorine (in the form of solutions, tablets or powder), which reacts with water killing pathogens and leaves a free chlorine residual. The effectiveness of chlorination depends on the correct dose of chlorine being added and on the absence of suspended particles in the water.




SODIS

Solar water disinfection is a procedure where water is treated using sunlight and readily available transparent plastic bottles. The method consists in filling the bottles with contaminated water, and exposing them to sunlight for at least 6 hours, so that the UV radiation and heat from the sun kills potential pathogens. Although simple, it can only be used in relatively clear water, and therefore water of high turbidity must be filtered before SODIS treatment.




PUR

PUR (Purifier of Water) is a powdered mixture that combines both disinfection and flocculation principles: the disinfectant agent kills bacteria, while the flocculants remove suspended solids by amassing them in clumps that sink to the bottom. The method is simple and quick, as it only requires pouring the powder into the water, stirring well for 5 minutes, and waiting another 5 minutes before filtering the water through a piece of cloth to remove the clumps. Nonetheless, it has an important cost, which could be a limitation in the long term.





FILTRATION METHODS
 

CLOTH FILTRATION

Filtering water through a fine-woven cloth is a simple method that can help reduce pathogen count, in particular cholera-causing bacteria and guinea worms. It consists in placing the cloth filter on top of a water vessel and pouring the water through it, so that bigger particles, and microorganisms attached to them, are retained. However, the treated water is not perfectly safe, since many bacteria and viruses can pass through the cloth’s pores. Besides, the cloth needs to be regularly rinsed and dried in order to remove accumulated particles.



 

CERAMIC FILTERS

Ceramic filters are candles or pots made of porous materials such as clay and have traditionally been used to reduce turbidity, but they may also remove parasites as well as some bacteria. The method consists in filling the ceramic filter with water, which passes through its pours into a bottom container. Although simple in operation, ceramic filters require important maintenance, since they need to be cleaned regularly in order to remove the accumulated material and restore the normal water flow rate. Besides, due to their fragility, they can break during use, resulting in poor removal of particles and microbes.




BIOSAND FILTERS

BioSand filters are an adaptation of the century old slow sand filtration process, and are designed as cylindrical barrels with sand and gravel layered inside. When water is poured into the top of the BioSand filter, it slowly drops through the holes in the diffuser and flows down through the sand and gravel layers, where pathogens and suspended solids are removed, until the treated water flows out of the outlet tube. It is an effective way to remove disease-causing microorganisms, as well as harmful chemicals (e.g. iron, manganese and sulphur). However, it requires important initial, transportation and installation costs.

BUCKET FILTERS

Bucket filters are a type of rapid sand filters consisting of two buckets, the first one filled with layers of sand and gravel and with a perforated bottom. When water is poured into the first bucket, it flows rapidly through the media layers into the second bucket. Due to their high filtration rate, the pathogen removal efficiency of bucket filters is low, and therefore require the use of chemical coagulants before. In addition, they require some backwashing every few hours in order to remove accumulated particles.

LIFESTRAW FILTER

LifeStraw is a recent invention designed to be used by one person, where water is drunk straight through the straw. When water is drawn up, it passes through hollow fibres that filter water particles, while bacteria and parasites are trapped. The filter can be easily cleaned by blowing air out the straw. This method is effective and instant, but too expensive to be used in a long-term.

By Fatine Ezbakhe
Civil Engineer specialized in Water

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Taxonomy

• Treatment
• Household Water Treatment
• Purification
• Households Treatments
• Water Treatment Solutions
• Contaminant Removal
• water treatment

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