A Monitor's Guide to:
Collecting Municipal Supply Samples for Bacteriological Monitoring of Water Quality.
A. Rationale & Scope:
The usual source of water borne diseases is faecal or sewage contamination of drinking water. Municipal water utilities ensure bacteriologically safe drinking water through a multi-step process involving filtration and disinfection to remove particles and disinfection to kill bacteria, viruses, and parasites. Common disinfection methods include adding chemicals like chlorine or using ultraviolet (UV) light. The water is then protected with sufficient residual chlorine and monitored throughout the distribution system to confirm it remains safe for consumption. Bacteriological monitoring municipal supply at the consumer-end confirms that treatment processes have been effective and checks for potential contamination within the distribution network.
Bacteriological monitoring of municipal water supply at the consumer end involves collecting samples and testing them for the presence of indicator bacteria, like coliforms and E. coli, to ensure the water is safe for consumption. Careful sample collection is the first step for effective bacteriological monitoring of municipal water supplies, as improper collection can lead to contamination and inaccurate results. Other critical steps include transporting samples in sterile containers, prompt laboratory analysis, and interpreting results against established standards.
Bacteriological monitoring of municipal water supply at the consumer end involves collecting samples and testing them for the presence of indicator bacteria, like coliforms and E. coli, to ensure the water is safe for consumption. Careful sample collection is the first step for effective bacteriological monitoring of municipal water supplies, as improper collection can lead to contamination and inaccurate results. Other critical steps include transporting samples in sterile containers, prompt laboratory analysis, and interpreting results against established standards.
B. Field Sampling Materials:
For proper sampling, you will need; (a) 250 ml clean & sterile bottle with added dichlorination agent (sterile sample collection bottle), (b) gel ice packs, c) portable ice box or pick up bags and self-locking cable ties, (d) water resistant permanent marker, and (e) sample collection record form.
1. Clean & Sterile Sample Collection Bottles:
A clean and sterile bottle is necessary for municipal water samples to prevent contamination, which could lead to inaccurate bacterial analysis results. Preexisting contamination in nonsterile bottles can give rise to false positive test result. Any bacteria or other microorganisms present in a non-sterile bottle could be mistaken for contaminants in the water sample. False positive means that test is positive for faecal contamination even if there was no contamination in municipal supply. False positive results can defeat the very purpose of checking for quality of municipal supply. On the other hand, dirt in a sample bottle can affect bacteria in the sample by introducing new bacteria, interfering with the existing ones, or altering the sample's chemical and physical environment. This contamination can lead to inaccurate test results. Similarly, detergents residue in a sample collection bottle can kill or hinder growth bacteria of interest in the sample. Hence, proper cleaning and rinsing of sample collection bottles is critical to avoid contamination and ensure accurate results. Thus, use of Clean and Sterile bottle is mandatory for collection of municipal supply samples for bacteriological analysis.
Figure 1: Sterile Sample Collection Bottle and Sample Collection Record Packed Inside.
About 250 ml of water sample is adequate for bacteriological analysis. Although, larger size clean & sterile bottles can be used, they would add to the burden of packing, storage and transportation to laboratory. Larger bottles would be justified when samples are collected for chemical analysis in addition to bacterial analysis.
The purpose of sampling for bacterial analysis is to detect if there is any faecal contamination of municipal water at the consumer-end, despite various measures taken by the water utility. If residual chlorine in the sample is allowed to remain as it is, the chlorine may kill faecal bacteria in transit and laboratory analysis may give a false negative result. A false negative result in a bacterial analysis of municipal water supply means the test wrongly passes the sample as microbially safe, even though faecal contamination was actually present at the time of collection of the sample. To minimise the possibility of false negatives, a little bit of sodium thiosulfate is added to sample collection bottles to neutralize the residual chlorine. This ensures the lab accurately measures the original microbial content of the water, rather than a sample that has been disinfected by the residual chlorine.
The IHS Laboratory provides clean & sterile sample collection bottles with added sodium thiosulfate to collect samples for bacteriological analysis.
2. Gel Ice Packs (Cool Packs):
water-based gel that can be frozen. The gel inside the pack is a mixture of water, a thickening agent, and a non-toxic dye. The pouch is typically made of puncture-resistant plastic to prevent leaks. These can be reused many times, until the seal is intact and polythene not punctured. Frozen cool packs are necessary to keep collected samples cool during transport from field to the laboratory. Cool packs are available in various sizes from several manufacturers.
Figure 2: An Assortment of Gel Ice Packs (Cool Packs).
Cool packs ought to be frozen in advance for use on the day of sample collection. Place the cool packs flat in the freezer compartment of household refrigerator, the night before the date of sample collection.
Figure 3: Place Gel Ice Packs in Freezer Compartment.
Cool packs are flexible in normal room temperature. When frozen, the cool packs become rigid. If these bags are kept upright, the bags bulge as the gel inside settles under gravity. When frozen upright cool bags can end up frozen in irregular shapes. Packing or wrapping of sample bottles with irregularly shaped frozen cool packs would be difficult. Hence, it is advisable to freeze cool packs in horizontal position by stacking one above the other.
Figure 4: Cool packs would freeze in irregular shapes, unless placed flat.
3. Portable Ice Box or Pick Up Bags & Self-locking Cable Ties:
Portable ice box or polythene pick up bags are required to preserve and carry collected samples from field to laboratory. Frozen gel ice packs are placed inside the ice box to keep the sample bottles cool. As ice boxes come with a cover, the samples are protected from exposure to sunlight. If portable ice box is not available or is not feasible, polythene pick up bags can be used. Black pick up bags would be preferable but any dark colour polythene bags can be used. Choose a bag of an appropriate size to fit the sample bottles and cool packs, leaving enough material at the top for a secure tie or knot to prevent shifting during transit. Self-locking cable ties can be used to tie the pick-up bag, to ensure closed contact of frozen cool pack with the filled sample bottles and to prevent shifting of the bottles during transit.
Figure 5: Portable Ice Box Or Polythene Pick Up Bags & Cable Ties, for Transportation of Sample to Laboratory.
4. Sample Collection Record Form:
A sample collection record is a must for every sample that is collected. This record must show the Bottle Id, which is a unique Id assigned to the sample collection bottle by the laboratory. Figure 5 shows a snippet of water sample collection record form. The form can be downloaded from IHS Lab website. Information regarding the date, time and place of collection water sample should be provided in this record. The sample collector should describe in his/her words the source from which the sample was collected.
As far as possible the Customer Account Number (CAN) of the metro water connection should be mentioned. The CAN number serves as a unique identifier for each water customer, linking them to their address, registered mobile number and account information. This 9-digit number is essential for filing complaints. The most straightforward way to find the CAN number of household is to look for the CAN on the water bill (Figure 6). This will facilitate registration of complaints with the Hyderabad Metro Water Supply & Sewerage Board (HMWSSB), in case bacteriological analysis shows signs of faecal/sewage contamination.
Figure 6: Water bill snippet showing CAN number.
Items ate serial 3, 4 and 6 are optional.
Record GPS coordinates if feasible. If you are sending WhatsApp current location to IHS Laboratory, mention the Bottle Id of sample.
Samples are to collected in sterile bottles provided by the laboratory.
Similarly, share photos of the sampling spot and its surroundings, if feasible. Photos help in interpretation of test results, particularly if bacteriological analysis shows signs of faecal contamination.
In the unlikely event of any other bottle used to collect the sample, use the space at Line item 4. ‘About sample collection bottle’ to record details about the sample collection bottle. This line can be left blank in cases were sterile bottles provided by the IHS laboratory are used.
Figure 7: A Snippet of Water Sample Collection Record (WCR1) to Illustrate Essential Elements of the Form.
5. Water Resistant Permanent Marker Pens (Laboratory Marker Pens):
A medium tip (0.8 to 1.5 mm) water resistant permanent marker pen is required for writing information about sample collection date & time on the label affixed to sample collection bottle.
Figure 8: Assorted Permanent Marker Pens.
C. Prepare and Plan Before You Start Sample Collection Work:
1. Ready the sample transport container (ice box or pick up bags):
Retrieve the frozen cool packs from refrigerator and place them in the ice box or pick up bag. Carry enough sample collection bottles according program.
2. When and Where to Collect Samples?
Collect municipal water samples for bacteriological analysis during the course of testing for residual chlorine. Live supply of municipal/metro water should be tested for residual chlorine. This is because we want to check if the metro water supply has been well-protected during transit from treatment plant / service reservoir to consumer premises. Sufficient residual chlorine in municipal water would imply that treated water must have been protected from contamination, during transit in the distribution system. This is because adequate concentration of free chlorine will continue to kill any bacteria, viruses, or other pathogens that may have entered the water supply.
If residual chlorine is low (less than 0.5 mg/L) at household water connections, it indicates potential contamination, making bacteriological analysis crucial. Collecting 4 to 8 water samples for bacterial testing is a standard procedure to confirm the safety of the water supply. This approach is important because low chlorine levels may not be sufficient to kill pathogens, especially when water is susceptible to re-contamination.
The bacteriological analysis will reveal if disease-causing microorganisms are present in the water. The number of samples (4 to 8) is chosen based on the program's target to get a representative picture of the water quality throughout the locality. The samples must be taken from locations that are representative of distribution network and points-of use in the concerned locality/slum.
3. Wash your hand before starting RC testing & sample collection work:
Clean hands are a fundamental part of the overall process, which also includes steps like flushing the tap and using sterile bottles to maintain sample integrity. Dirty hands can transfer bacteria, fungi, and other microorganisms to the water sample. Washing of hands ensures the sample being tested reflects the actual bacterial quality of the water source, not the bacteria from the person collecting it. If hands are not clean, the test may incorrectly show contamination, when the water supply is actually safe, resulting in a false positive.
Figure 9: Proper Hand Washing - Steps.
First, wet both hands with clean, running water and apply a little soap. Then, scrub all surfaces of your hands, including the backs, between your fingers, and under your nails, for at least 20 seconds. Rinse your hands thoroughly under clean, running water. Finally, dry your hands with a clean towel/cloth/handkerchief or air dryer.
D. Steps in Collecting Sample for Bacteriological Analysis:
1. Have the sterile sample collection bottle ready:
Open the polythene packing immediately before sample collection. Do not use the bottle if the polythene cover is broken, cap of the bottle inside is loose or is cracked, the bottle looks dirty or there is any other condition that that makes you doubt if the bottle is really clean and sterile.
Label the bottle using water resistant permanent marker pen. Bottle should be labelling before filling it with samples. You may fill the sample collection record after collecting the sample.
2. Flush the tap and reduce flow:
By this time, you would have flushed the tap for a couple of minutes before the RC test. Make sure a bucket or container is under the tap to minimise wastage of water, avoid splashing onto your clothes and/or spreading of on to your foot wear.
Flush the tap for a couple of minutes more and then reduce the water flow to a slow, steady pencil like stream to avoid splashing. The flow should be slow enough, to ensure there is splashing at the time of filling the sample collection bottle.
Figure 10: Place a bucket, Flush tap and Reduce flow to a smooth stream.
3. Open the sterilized bottle just before collection:
- Hold the bottle in one hand and open and hold the cap in the other hand avoiding to touch inner side of the cap. Do not touch the inside of the cap.
- Do not turn inner side of the cap upwards, as this may allow blown particles to settle on it. Do not touch the inside of the sample bottle.
- Do not rinse the bottle. The bottle contains some liquid or powder to remove residual chlorine, if any. Do not turn the bottle downwards! Recall that the laboratory adds a little bit of de-chlorination agent into the sample collection bottle to neutralize residual chlorine in the municipal supply. Inadvertent downward tilting of the sample collection bottle may result in the added regent to fall out of the bottle.
4. Fill the bottle:
Fill the bottle to the base of the neck. Allow a little air gap to remain. Rinsing and overfilling may wash out the dechlorinating agent inside the bottle. Hence, do not rinse the bottle, and do not overflow it.
5. Cap the bottle and place in transport container:
Immediately cap the bottle tightly without allowing the tap or water to touch the inside of the bottle or cap. Keep the bottle inside ice box or pick up bag containing frozen cool packs.
6. Fill out the sample collection record.
7. Deliver to laboratory as soon as possible, preferably within six hours from the time of collection of first sample.
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To pick up sample collection bottle and/or schedule collection of samples: Email: ihslab@ihs.org.in with your address and contact telephone; OR WhatsApp: +919848011251; Or Call: 23211013/4.