Water Borne Diseases & Prevention Through Good Plumbing Practices

Transcription

1 INDIAN PLUMBING TODAY Water Borne Diseases & Prevention Through Good Plumbing Practices Sharat V. Rao Water is the elixir of life and life cannot sustain without it Preface The term Water Borne Diseases is reserved largely for infections that are predominantly transmitted through contact with or consumption of infected water. Water borne diseases easily transmit when contaminated water is used for any of the following purposes in day-to-day living: Drinking Washing vegetables & fruits Making ice cubes Brushing teeth Mouth rinsing Other sources for transmission are also prevalent especially in hospitals and surgical procedures. When transmission of contamination is not prevented and controlled, it can reach epidemic limits especially in urbanised areas due to the dense population and restricted immunity levels. Source of Water Water, chemically known as H 2 O is never pure. It dissolves ionic compounds as it comes in contact with the ground surface or with mineral formation when percolated through the earth. It also contains dissolved gases and dust picked up when falling through the air as rain, snow or hail. Water is classified as Surface Water when extracted from sources such as lakes or river and ground water when obtained from streams, well or aquifers originating underground. The major source of water for us are the lakes and rivers on a macro scale and public mains or wells on a micro scale, such as township developments. The immediate source are public mains and wells, both having great potential to get polluted. Water Quality Standards Water, before it reaches the consumer taps has to be of a quality acceptable for drinking. Water MAY

2 quality standards have been well established and in India IS elaborates the water quality standards required for drinking purposes. Majorly three basic characteristics govern water quality, such as physical, chemical and bacteriological. The physical and chemical characteristics do not contribute directly to water borne diseases, although their presence above the prescribed limits is harmful to the general health. The biological and micro-organic characteristics are the direct indicators. Coliform / E-Coli should not be present in the water which are the immediate indicators of possible contamination from drainage. Water Borne Diseases Bacteria, virus and protozoa groups are the microorganism groups containing pathogens of primary concern in the study of water borne diseases. The most common water borne diseases are :- 1) Typhoid 2) Cholera 3) Dysentery 4) Hepatitis 5) Giardiasis 6) Polio 7) Legionellosis Legionellosis is not very common in our country but has made an impact in Western countries like UK and USA. This is caused by a bacteria belonging to genus legionella and in most cases, it is caused by legionella pneumophila. This disease is associated with severe symptoms such as fever, chills, pneumonia etc. The effect that legionella has on the lungs is deadly and if not diagnosed correctly, can be fatal. Treatment of Water Treatment of water at source and storing the same for further distribution form a part of water distribution. The treatment will essentially comprise of: a) Screening : If the supply is from surface water, a coarse or fine screen is usually placed at the intake. Coarse screens are usually made of 15 mm diameter bars with a clear opening of 25 mm to 75 mm. Fine screens will have opening of approximately 10 mm. b) Clarification : Clarification of water allows suspended impurities present in the water to settle down by gravity. These basins are generally made of R.C.C. construction rectangular or circular in plan. In many instances, clarification or sedimentation is coupled with coagulation. Coagulants are certain chemical components which when added to water and properly mixed form gelatinous precipitates called 'floc.' This aids in easy settlability. The most common coagulants are alum and iron salts like ferrous and ferric chloride. c) Filtration : Screening and sedimentation removes a large percentage of suspended solids, organic matter and colloidal solids. But still the resultant water will contain fine suspended particles which are removed by filtration. Filtration in simple words is passing the water through beds of granular materials called filters. Two types of filters commonly used are: i) Slow sand gravity filter ii) Rapid sand filter There is a third type of filter which works under pressure and is known as Pressure Filter. These are generally used for small plants. Filter materials generally used are sand, gravel, coal, anthracite etc. d) Disinfection : The methods mentioned so far were physio-chemical processes which do not eliminate bacteria, the main carrier for water borne diseases. Disinfection is usually accomplished by chlorination, UV radiation, ozone generation and boiling of water. e) Chlorination : Chlorination is one of the most commonly adopted methods for disinfection. The basic advantage is that they are cheap, easily measurable and capable of providing residual effects for a longer period. The amount of chlorine required depends on how impure the water is. The amount of chlorine used is the 'Chlorine Demand.' After the chlorine demand is fulfilled and the maximum kill is effected, free chlorine will appear as residual. It is recommended to have about mg/l as free residual. MAY

3 INDIAN PLUMBING TODAY The forms in which chlorine is adopted are : 1) Liquid chlorine / chlorine gas 2) Hypochlorites or bleaching powder It is important to have a contact time of at least 30 minutes i.e. supply of water after chlorination to reach the first consumer should take at least 30 minutes. f) Ultra Violet Radiation (UV) : UV rays are invisible light rays having wave length of 1000 to 4000 mm. They can be produced by passing electric current through mercury enclosed in quartz bulbs. These rays are highly effective in killing all types of bacteria, thus yielding truly sterilised water. This method is best used in treating small quantities of water as they are expensive. Water should be free from turbidity and suspended or colloidal matter. The advantage is that pathogen kill is immediate and effective but certain viruses may be resistant. The disadvantage is that there is no residue and so post chlorination, to maintain minimum ppm chlorine will be required. They are very effective for hospitals, restaurants / hotels and individual households. g) Ozone : Ozone represented as O 3 readily breaks down to normal oxygen and release nascent oxygen as below O 3 O 2 + O This nascent oxygen is a powerful oxidising agent and is very effective in disinfecting water. The dosing and control is very difficult and like uv, there is no residual. It is very expensive and is hence used only for small applications in India, like for disinfection of swimming pool water or in the manufacture of bottled water. h) Boiling : It is a very effective method of disinfection and can be used as a household remedy. It is advisable to boil the water before consumption especially during monsoon and when there is an epidemic. This is the most simple method without any reliance on any type of chemicals or rays. Good Pluming Pratices While the importance of source water treatment to ensure safe drinking water seems obvious, the need to safeguard the purity of water when it enters the distribution system is also of prime importance. Following good plumbing practices will go a long way in protecting the building occupants. Some of the frequently observed lacuna in design or installation are as below: Improper storages Faulty distribution system Cross connection & backflow Lack of maintenance a) Improper Storages Generally, all buildings in India have an underground storage tank into which, the water from the public mains is fed, through a water meter. These inlet connections pass through open drains and the faulty joints are a source of contamination. Further, in majority of the construction, the top of the water tank is below the grade level and the overflow pipe is connected to the nearest storm water drain. The storm water drain is subjected to abuse leading to accumulation of filth and debris which, during monsoon season, is a potential contamination threat. There is every possibility that the polluted water will backflow into the tank and contaminate its contents. b) Water Distribution 1) Dead legs in pipe branches and laterals must be avoided. These are potent areas for sediments to be lodged which encourages bacteria breeding. 2) Water pipe must be laid above the sanitation pipes and should be separated by vertical distance of at least 600mm, to avoid infiltration of sewage into water lines through faulty joints. 3) Periodic and systematic flushing of the entire distribution system should to be done. This will ensure that the chlorine residual moves to all parts of the piping networks and dead legs (if any) are also flushed. MAY

4 4) Flushing of the entire distribution system network with chlorine solution of strength 50 ppm should be done after installation and before regular supply is initiated. 5) For hot water system, it is recommended to maintain a temperature of above 51 0 C in hot water return piping and 54 0 C for storage in circulated water heaters, to prevent legionella. 6) Scale or mineral build up in the pipeline & faucet heads happen due to hard water. This encourages the build up of pathogens. The water needs to be passed through softening units before entry into the distribution system. c) Cross Connections and Backflow A lot of articles on this subject are in circulation along with coverage in papers presented in IPT. This clearly underlines the importance of this subject, although still neglected, in actual practice, 1) Cross Connection A cross connection is defined as an actual or potential connection between the public water supply and a source of contamination. Source of the most common cross connections encountered in plumbing systems are :- ii) Over-rim connections Another frequently observed connection is one wherein the water supply terminates above the flood level of a fixture but there is a hose pipe that is submerged as in the case of telephone/ flexible shower in a bath tub, as shown in Fig. 2a and 2b. Fig 2a Fig 2b iii) Direct Cross Connection Sometimes, there are some cross direct connections, where the potable water line is directly connected to a pipeline or pressure tank that contains non potable substances (for example in factories). Another typical example is potable water servicing a lawn sprinkler, very common in bungalows. See Fig. 3a and 3b. i) Under-rim or Submerged connections This happens when the water inlet is terminated into bottom or side of a receptacle that is immersed in a polluted or contaminated substance. A common example is a water inlet from public supply submerged into the fire tank. Although fire water is normally not contaminated, still it can be a potential hazard. See Fig. 1. MAY

5 INDIAN PLUMBING TODAY iv) Backflow Backflow or back siphonage is siphonic action in an undesirable or reverse direction. It is typically caused by the force of atmospheric pressure exerted against a contaminated or polluted liquid, forcing this liquid towards the potable water system that is under lower pressure. A classic example is a case where the water main happens to run below the sewage carrying pipe. In most of the places we have interrupted water supply i.e. water is only supplied for a few hours in a day. The water pipe turns dry when supply is stopped. If there is a leak in the sewerage line, the sewage can be back siphoned into the water line especially at faulty joint locations. Therefore, it is mandatory to run the water line at least mm above the sewage line. See Fig. 4. Hospital equipments Drinking water fountains Irrigation systems HVAC equipment Boilers d) Backflow Prevention The most simple way to prevent the occurrence of backflow is to provide air gap. This is applicable both to water supply and drainage system Air Gap: By definition, an air gap in a water supply system is the unobstructed vertical distance through the free atmosphere between the lowest opening from any pipe or faucet supplying water to a tank, receptacle or any other device and the flood level rim of the receptacle. See Fig. 5a and Fig. 5b. FAUCET AIR GAP AIR GAP FLOOD LEVEL BATH TUB 2) Potential sources of cross connections and backflow Some of the frequently encountered Cross Connections in plumbing of buildings are as under: Flush valve connections to Water Closets. This is a potential backflow hazard especially when the flushing and drinking water connections are taken from the common pipe. Food and beverage dispenser Dishwasher connections Hand shower Fig 5a FLOOR LEVEL LAVATORY FLOOD LEVEL Fig 5b Air gaps are also provided in the drainage system and such connections are called 'Indirect Waste.' As the name suggests, an indirect waste does not permit a connection to be made directly into the drainage system and the waste will be essentially connected indirectly, through an air gap. These are very commonly used in food handling equipments and devices, drinking water fountains, hospital equipments, laboratory and commercial kitchen sinks (slop sink) etc. MAY

6 manufactured locally and have to be imported. It is essential to terminate the inlet connection with an air gap and to have a non return valve or a backflow preventer. Many times, the air gap is not achieved and the inlet terminates in a submerged condition which wil promote the backflow of water from the water tank into the public main during no flow conditions in the inlet line. No flow condition is a common occurrence as the public supply is intermittent, return lave is also absent aggravating the condition still further. Further, in majority of the construction, the top of the water tank is below the grade level and the overflow pipe is connected to nearest storm water drain. The storm water drain is subjected to abuse leading to accommodation of filth and debris which during monsoon season is a potential contamination threat. Maintenance Lack of maintenance or total absence of any form of maintenance especially in housing societies has become a major issue. The present trend is to use recycled treated sewage for non potable applications. These sewage treatment plants are badly operated and maintained leading to bad quality water finding its way to the consumer end. The storm water drains are seldom cleaned thus resulting in flooding during monsoon. Sanitary drains also need periodic maintenance to create good hygiene environment. Broken manhole covers are a common occurrence adding to the menace. Indirect waste connections are also to be provided for drains, overflow or relief pipes from potable water pressure tanks, water heaters, boilers etc. The basic intention is to prevent the possibility of waste backing up to where the food is placed and contaminating it. See Fig. 6a and Fig. 6b. Nowadays there are Backflow prevention devices available which can be used. These are available as pressure type or atmospheric type. These are not Conclusion As our cities expand the threat of water borne diseases looms large. Awareness to stop the abuse of water has to be stepped up with more interaction on the social media. Ensuring proper plumbing practices through legislation and codes is required. Sharat Rao has a wide range of experience in the field of design and project management consultancy in water and wastewater treatment, and utility services such as water supply, drainage, firefighting and irrigation. He is the Managing Director of Engineering Creations Public Health Consultancy Pvt. Ltd., a firm based in Mumbai. He can be contacted at: svr@ecphc.com MAY