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Hygiene and Environmental Health Module: 14. Treatment of Drinking Water at Household and Community Level

Study Session 14  Treatment of Drinking Water at Household and Community Level

Introduction

Water has always played a prominent role in human civilisation. Water was, and continues to be, needed for drinking, preparing food, bathing, cleaning, irrigating crops and a variety of other tasks. Having ready access to water, therefore, has always been important. However, the water sources used for supplying water were not always clean. Treating drinking water to improve smell and taste and to remove disease-causing organisms has been necessary throughout human history.

Water must look and taste clean, i.e. have eye appeal and taste appeal, if we are going to want to drink it, and it must also be safe to drink. Water is the breeding ground for an unbelievably large variety of organisms that get into water through a variety of routes. Microbial contamination is the most common and widespread health risk associated with drinking water; therefore treatment of water to eliminate pathogenic microbes is of vital importance. In this study session, you will learn about the public health significance of water treatment, the characteristics of raw (untreated) water that determine the treatment methods, types of household/community–based water treatment and a selection of treatment processes.

Learning Outcomes for Study Session 14

When you have studied this session, you should be able to:

14.1  Define and use correctly all of the key words printed in bold. (SAQs 14.1 and 14.5)

14.2  Explain the purpose of water treatment at household, community and municipality levels. (SAQ 14.2)

14.3  Describe the methods of water treatment at household and community levels. (SAQs 14.3 and 14.4)

14.4  List the stages of large-scale (municipal) water treatment. (SAQ 14.5)

14.1  Waterborne diseases

Diarrhoea, infectious hepatitis, typhoid and paratyphoid enteric fever are all examples of waterborne diseases that are common problems in our country. These are all caused by microbial contamination. Lead poisoning and fluorosis, caused by chemical contamination, are also classified as waterborne diseases.

  • What distinguishes waterborne diseases from other types of disease associated with water?

  • Waterborne diseases are caused by consumption of water that has been contaminated by human or animal wastes, or chemicals. Other types of disease may be caused by external contact (water-based), or infection by an insect vector (water-related), or by limited availability of water for washing (water-washed).

Waterborne diseases can also be classified in a different way as either acute (short-lived) or chronic (long-lasting). Acute health effects occur when the levels of some contaminants in drinking water are high enough to cause acute (immediate) health effects within hours or days of consumption, for example, vomiting. Chronic health effects occur after long-term exposure to a contaminant that may be present only in small amounts. Examples of chronic health effects are liver and kidney damage.

14.1.1  Causes of waterborne disease outbreaks

There are a lot of possible causes for an outbreak of waterborne disease. The use of untreated spring water and surface water, and inadequately or interrupted disinfection of surface water, spring water and well water may all be responsible. These are all causes associated with the source of water but other problems can arise at points in the system after the source. For example, cross-connections of pipework, contamination of water in the household, contamination during the construction of water source protection, contamination of storage facilities including private storage tanks are all contributors. Consumption of water that was not intended for drinking, contaminated bottled water and ingestion of water while swimming are also possible causes.

14.2  Water treatment

The purpose of water treatment is to reduce or remove all contaminants that are present in the water and to improve water quality so that it is completely safe to drink. Water is unlikely to be completely free of contaminants at the original source. The types of water treatment processes depend on the characteristics of the raw water (untreated water direct from its source) and required water quality standards. Suspended solids, bacteria, algae, viruses, fungi, minerals such as iron and manganese, and fertilisers are among the substances that are removed during water treatment. (Suspended solids are tiny particles of solid material that are carried along or suspended in the water.) Effective treatment should ensure the removal of all disease-causing agents and so reduce the possibility of the outbreak of waterborne disease.

Water treatment systems can be categorised as small-scale water treatment, which includes community and household treatment methods, or large-scale water treatment that might be found in towns and cities.

14.3  Small-scale water treatment systems

Household- and community-level treatment systems are the methods most likely to be used in rural areas.

Household-level water treatment is appropriate when:

  • A relatively small amount of water is obtained from a well or spring and is collected and transported by hand.
  • The source is contaminated and simple protective measures can neither improve water quality nor stop the contamination.
  • Community resources are inadequate to meet the cost of a simple community treatment system and make it difficult to develop a centralised treatment system.
  • An emergency situation causes disruption of the service and contamination of the water supply so that a long-term rapid solution is needed.

Community-level water treatment is appropriate when:

  • A water source serves a larger population than can be served by household level or individual treatment systems.
  • A community water source is contaminated and simple protective measures can neither improve water quality nor stop the contamination.
  • Community resources are adequate to cover the cost of construction, operation and maintenance of a simple community-level treatment system.

There are several different methods of small-scale water treatment that can be employed at the household and community level. Broadly speaking these can be grouped either as filtration methods, in which water passes through a porous barrier (filter) that traps tiny particles including pathogenic microorganisms and other impurities, and disinfection methods, in which contaminants are removed by the use of various chemicals or by energy from the sun.

14.3.1  Household sand filter

Household filters are an attractive option for household treatment because these filters can usually be made from locally available and inexpensive materials like clay pots or barrels. They are simple and easy to use. The upper pot contains layers of sand and gravel. Water is poured in at the top and, as it passes through the layers of sand, any particles within it are filtered out. The thickness of the layers should be approximately 5 cm of gravel, 5 cm of coarse sand and 10 cm of fine sand. The bottom of the upper pot should be perforated (have tiny holes in it) so the clean water can drip into the lower pot. The lower pot should have a tap (faucet) to draw off the clean water easily (see Figure 14.1). The sand and gravel should be changed when the rate of filtration starts to slow; at minimum it should be changed every two or three months.

Household water filter
Figure 14.1  Household water filter using two clay pots placed on top of each other.

14.3.2  Cloth filtration

Cloth filtration
Figure 14.2  Cloth filtration. (Source: International Federation of Red Cross and Red Crescent Societies, 2008, Household water treatment and safe storage in emergencies)

Cloth filtration is a common water treatment technique that is easy to use and inexpensive (Figure 14.2). Cloth filtration can be very effective against cholera, guinea worm (dracunculiasis) and other disease-causing agents. By following the procedures and practice yourself, you can demonstrate this for communities you are working with. The steps in cloth filtration are:

  • Use a large cloth, preferably made of finely-woven cotton. The cloth must be big enough to easily cover the opening of the container once it has been folded.
  • Fold the cloth at least four times so there are multiple layers of fabric and place this over the opening of the storage vessel.
  • Fasten the cloth securely around the rim of the opening and tighten the string. If reusing the cloth, always use the same side up each time.
  • Filter all water immediately at source as it is being collected.
  • Always keep filtered water separated from non-filtered water.
  • Rinse the filter cloth after each use, with a final rinse using cloth-filtered water, and then leave the cloth in the sun until it is dry.
  • Clean the cloth regularly using soap and replace it as soon as there are any visible tears or holes.

14.3.3  Other filtration methods

There are other filtration methods such as ceramic filters and biosand filters that are not currently widely used in Ethiopia but are also appropriate for household and community use.

Micron is another name for the micrometre–which is one millionth of a metre, i.e. a thousandth of a millimetre.

Ceramic filters of various types have been used for water treatment throughout the world. The majority of bacteria are removed mechanically through the filter’s very small (0.6–3.0 microns) pores. Ceramic filters are easy to use, relatively low cost and have a long life if the filter remains unbroken. They are good for reduction of bacteria and protozoa but lack residual protection so recontamination is possible.

Biosand filter
Figure 14.3  Biosand filter. (Source: as Figure 14.2)

Biosand filters differ from the other types of filter described above in that they make use of biological activity as well the mechanical filtering of particles. The most widely used version of the biosand filter is a concrete container about one metre in height and filled with sand (Figure 14.3). The container is filled with water so the water level is above the sand layer. The water allows a ‘bioactive’ layer to grow on top of the sand. This bioactive layer consists of algae, plankton and other microscopic plant life that helps reduce disease-causing organisms, particularly protozoa and bacteria. The biosand filter is fairly easy to use, can be produced from locally available materials, needs little maintenance and has a long life but it has a high initial cost and is difficult to transport. It will improve the look and taste of the water and is good for removing protozoa but has a low rate of virus inactivation and does not remove 100% of bacteria so recontamination is possible.

14.3.4  Solar disinfection

Solar disinfection, also known as SODIS, relies on energy from the sun to kill pathogenic organisms, especially bacteria. Ultraviolet light from the sun is an effective bactericide for water.

Turbidity is a measure of the cloudiness of water. It is caused by very small particles (suspended solids) that are individually too small to see with the naked eye.

This simple technique requires only a few plastic bottles and sunlight. Firstly, collect several bottles (0.3 to 2.0 litre) made of clear plastic, remove all labels and wash them thoroughly. Fill the bottles with water of low turbidity and shake for about 20 seconds to aerate the water. Expose the bottles to the sun by placing them on a roof or rack for at least six hours (if sunny) or two days (if cloudy) (see Figures 14.4 and 14.5). The water is now ready to drink.

Solar disinfection
Figure 14.4  Solar disinfection. (Photo: Eawag)
The SODIS method of water treatment
Figure 14.5  The SODIS method of water treatment. (Source: Eawag)

The benefits of solar disinfection include:

  • proven reduction of bacteria, viruses and protozoa
  • acceptability to users because of the minimal cost to treat water, ease of use and minimal change in water taste
  • unlikely recontamination because water is consumed directly from the small, narrow-necked bottles (with caps) in which it is treated.

The drawbacks include:

  • requires relatively clear water (if the water is too cloudy it has to be filtered first)
  • only a limited volume of water can be treated at one time
  • the length of time required to treat it.

14.3.5  Chemical disinfection methods

There are several commercially available products designed for treating water at household level.

Chlorine solution

Chlorine solution, also known as sodium hypochlorite solution or bleach, is the most affordable, easiest to produce, and most widely available chemical for household water treatment. It is supplied in bottles and has easily interpretable instructions for use on the side of the bottle. Typically, the procedure is to add a capful of chlorine solution to a 25 litre water storage container, then shake and wait for 30 minutes chlorine contact time before drinking. Double dosing is advisable if the water is visibly dirty.

Contact time is the amount of time that elapses when two substances are mixed. Chlorine contact time means the time between the introduction of chlorine and using the water.

Aquatabs

Aquatabs are a specifically formulated and branded solid form of sodium dichloroisocyanurate (NaDCC) (see Figure 14.6). NaDCC is stable in Aquatabs form as a solid which gives it a longer shelf life and makes storage, handling and transport much easier than with liquid bleach. One Aquatab contains 67 mg of NaDCC and treats 20 litres of clear water. For visibly turbid water, two tablets per 20 litres are needed. It is very important to mix well and leave for 30 minutes contact time before consumption.

PUR

‘PUR Purifier of Water’ is the brand name of a combined flocculant and disinfectant product produced by Procter and Gamble (Figure 14.7). It is now on the market in Ethiopia although it may not be widely available across the country. PUR can be used to treat raw source waters with a wide range of turbidity and pathogen load. This water treatment chemical allows flocculation to take place and helps to remove Giardia and Cryptosporidium cysts that are resistant to chlorine disinfection. (A cyst is a dormant stage in the life cycle of some protozoa and bacteria that is resistant to adverse environmental conditions and therefore difficult to destroy.) PUR comes in sachets with one sachet needed to treat 10 litres of water.

Flocculation is a process in which suspended solids are removed from water and turbidity is reduced. The solid particles lump together to form ‘flocs’ which slowly settle to the bottom of the container. A flocculant is a substance that can be added to water to encourage this process.

Aquatabs
Figure 14.6  Aquatabs tablets for household water treatment. (Photo: Abera Kumie)
PUR
Figure 14.7  PUR Purifier of Water. (Source: as Figure 14.2)
Wuha Agar
Wuha Agar
Figure 14.8  Wuha Agar for household water treatment. (Photo: Abera Kumie)

Wuha Agar is a chlorine-based water treatment solution that is used in Ethiopia (Figure 14.8). The procedure is very similar to other chemical treatment methods. For a 20 litre jerrycan, add one capful of Wuha Agar, cover and shake. After 30 minutes contact time you can use it.

14.3.6  Boiling

Boiling is also an optional water treatment at household level. Boiling is a simple way of killing any ova (eggs), cysts, bacteria and viruses present in contaminated water. Water should be heated until large bubbles are continuously coming to the surface of the water. The disadvantage of boiling as a treatment method is that it requires large amounts of fuel, so cost may prevent people from using this method. Also, boiling may give an unpleasant taste to the water, which may be unacceptable, and very hot water can cause accidents in the home. Boiled water can become recontaminated once it has cooled.

14.4  Safe storage

Whatever type of treatment method is used, it is essential that water is stored safely and hygienically. Even if water has come from an improved source, this will not guarantee that it is safe because contamination can occur in the household due to poor storage and handling practices. The principal health risk associated with household water storage is the ease of recontamination, particularly where the members of a family or community do not all follow good hygiene practice. Safe storage is especially designed to eliminate sources of recontamination by keeping objects, including hands, out of the system.

Safe storage containers
Figure 14.9  Safe storage containers.
  • What is it about the two containers shown in Figure 14.9 that make them safe for storing water?

  • They both have lids which prevent dust and insects from falling in the water and they both have taps so people can take water without removing the lid or dipping their hands or a smaller container, which may be dirty, into the water.

It is important to recognise that unsafe water is not made safe just by using safe storage methods. Safe storage helps to ensure that post-treatment recontamination does not occur within the household.

14.5  Large-scale water treatment

Large-scale or municipal water treatment is not common in rural communities but you may find it in larger towns and cities where there is a network of pipes and pumps to distribute water from the treatment works. There are several steps in municipal water treatment intended to remove solids, kill pathogenic organisms and make water safe to drink. The main stages are usually aeration, sedimentation, coagulation, filtration and disinfection.

Aeration simply means to mix air with the water. It is used to remove volatile (easily evaporated) substances from drinking water. Air and water are put into contact with each other, i.e. air is bubbled through the water, so that the volatile substances are evaporated into the airstream and removed from the water. Aeration can be carried out in towers or aeration basins to provide the necessary contact time between air and water. Sedimentation is the settling out of comparatively heavy suspended material (suspended solids) in water because of gravity. The settling takes place in a quiet pond or a specially constructed tank (Figure 14.10). A minimum 24-hour retention time is necessary to have a significant reduction in suspended matter. (Retention time means the length of time the water is kept (retained) in the tank.) Sedimentation can be used alone or in combination with coagulation.

Sedimentation tank
Figure 14.10  Sedimentation tank at a municipal water treatment works. (Photo: Pam Furniss)

Coagulation is the formation of particles in a liquid by adding chemicals. Its meaning is similar to flocculation. The flocculant used in large-scale treatment plants is usually alum (hydrated aluminum sulphate). This chemical is mixed with turbid water and then allowed to remain still in a sedimentation tank or basin so that the larger particles, or floc, settle to the bottom.

Filtration is the removal of suspended material from water as it passes through beds of porous material. This is exactly the same principle as filtration methods at household level. Filters can be made of layers of sand, gravel or charcoal. Filtration cannot completely remove all bacteria.

Disinfection kills most harmful organisms including pathogenic bacteria. Without disinfection, the risk from waterborne disease will remain. Disinfecting agents include chlorine, ultraviolet light, ozone, iodine and others but, of these, chlorine is the most frequent treatment agent. The process is called chlorination.

14.6  Chlorination

Chlorination, used at both household and large-scale levels, is one of the most effective and widely used methods for disinfecting water and making it safe to drink. Whatever the level, it is important that the correct quantity of chlorine is added to remove all impurities.

  • Which of the water treatment methods described earlier for household use involve chlorination?

  • Three of the four chemical disinfection methods described are chlorination methods. Chlorine solution, PUR and Wuha Agar all use chlorine as the disinfecting agent.

At municipal level, various terms are used to describe aspects of the chlorination process. Chlorine dosage is the amount of chlorine added to the water system in milligrams per litre (mg/l). Chlorine demand is the amount of chlorine that combines with the impurities and therefore is no longer available as a disinfecting agent. The chlorine that remains in the water after the chlorine demand has been satisfied is called free chlorine residual. A certain amount of residual chlorine is a good idea because it protects against future recontamination.

The orthotolidine-arsenite test (OTA) is used to determine the amount of free chlorine residual. When orthotolidine reagent is added to water containing chlorine, a greenish-yellow colour will appear. The intensity of the colour is measured against a chart to determine the amount of free available residual chlorine in the water. The amount of residual chlorine needs to be in the range of 0.2–0.5 mg/l if it is to prevent recontamination with bacteria. The OTA test requires a special test kit. If required, this should be available from your district environmental health office.

The benefits of point-of-use chlorination include:

  • Chlorine is proven to be effective in the reduction of bacteria and most viruses.
  • The residual chlorine is effective in protection against recontamination.
  • It is easy to use.
  • Chlorine is easily available at low cost.

The drawbacks of chlorine treatment include:

  • It provides relatively low protection against some viruses and parasites.
  • Lower effectiveness in water contaminated with organic and certain inorganic compounds.
  • Potential objections to taste and odour.
  • Some people have concerns about the potential long-term carcinogenic effects of chlorination byproducts.

Summary of Study Session 14

In Study Session 14, you have learned that:

  1. Drinking water is treated to improve smell, taste, clarity and to remove disease-causing pathogens.
  2. If water from an unprotected source is not treated before it is used for drinking, this may cause an outbreak of waterborne disease. Disease outbreaks may also occur because of contamination at some point after collection from the source.
  3. The main objectives of water treatment are to:
    • reduce or remove all contaminants that are present in the water
    • raise water quality to the highest possible level for long-term use
    • meet water quality standards
    • reduce waterborne diseases.
  4. Household water treatment technologies include dilute bleach solution, Aquatabs, solar disinfection (SODIS), cloth filters, ceramic filters, the biosand filter, PUR and Wuhu Agar. Safe storage is also essential.
  5. Conventional large-scale water treatment is feasible for urban areas where the population is dense. There are several steps in the treatment process at this level.

Self-Assessment Questions (SAQs) for Study Session 14

Now that you have completed this study session, you can assess how well you have achieved its Learning Outcomes by answering the following questions. Write your answers in your Study Diary and discuss them with your Tutor at the next Study Support Meeting. You can check your answers with the Notes on the Self-Assessment Questions at the end of this Module.

SAQ 14.1 (tests Learning Outcome 14.1)

Match the phrases with the corresponding words.

Using the following two lists, match each numbered item with the correct letter.

  1. Process of treating with chlorine

  2. Time required to wait to drink after chlorination

  3. Water not yet treated

  4. Free residual available chlorine in treated water

  • a.Chlorine contact time

  • b.Chlorine residual

  • c.Chlorination

  • d.Raw water

The correct answers are:
  • 1 = c
  • 2 = a
  • 3 = d
  • 4 = b

SAQ 14.2 (tests Learning Outcome 14.2)

Suppose you went to a village to promote household water treatment. Mr. Abebe, a local farmer, asks you why he needs to treat the water for drinking. What would you say to him as an explanation?

Answer

Nearly all river and stream water may be contaminated with at least one of the three types of potentially disease-causing microorganisms, namely protozoa, bacteria and viruses. These can be removed by treating the water.

If Mr. Abebe used one of the methods of household water treatment he would be protecting his family and himself from many unpleasant, debilitating and possibly life-threatening diseases.

SAQ 14.3 (tests Learning Outcome 14.3)

Suppose you have a group of women in your area who want to know about household water treatment by chlorine solution, particularly Wuha Agar. What are the key points you would explain to them?

Answer

Wuha Agar is a type of chlorine solution that is commonly available. To use it you add one capful of Wuha Agar to a 20 litre jerrycan of water, replace the lid and shake. After 30 minutes of contact time you can use the water for drinking and other domestic purposes. This will kill bacteria and help to reduce diarrhoeal diseases.

SAQ 14.4 (tests Learning Outcome 14.3)

A man comes to see you and explains that his family obtains water from a protected water source and that it has been treated with chlorine. He asks you how he can find out whether the chlorine still protects his family or not. How could you find out if his water was still safe to drink?

Answer

You should do the orthotolidine-arsenite test (OTA) to measure the residual chlorine. The residual chlorine helps to prevent recontamination of pathogenic bacteria if it is between 0.2–0.5 mg/l.

SAQ 14.5 (tests Learning Outcomes 14.1 and 14.4)

Filtration and disinfection are important water treatment processes. Briefly describe each of these processes and explain their role in making water safe to drink.

Answer

Filtration means passing water through a layer of sand, gravel, cloth or other barrier that allows the water to pass through, but holds back any small particles. The particles may be dirt, soil and other contaminants including many pathogenic microorganisms that make the water unsafe to drink. However, some bacteria can pass through filters, so filtered water is not completely safe to drink.

Disinfection is a process for removing contaminants from water and killing most of the harmful microorganisms that may be present. It usually involves treatment with chlorine or other chemicals.