Chapter 4 Practical 5
Identify suitability of given water samples for various purposes using given kits
Aim:
To analyze different water samples using a rapid water testing kit for key physicochemical and biological parameters, and to determine their suitability for various purposes (drinking, domestic use, irrigation) by comparing the results with standard permissible limits.
Principle:
The suitability of water for a specific purpose is determined by its quality, which is defined by its physical, chemical, and biological characteristics. Different uses have different standards:
Drinking Water: Requires the strictest standards (e.g., BIS IS 10500:2012, WHO guidelines) with very low limits for contaminants, especially pathogens and toxic chemicals.
Domestic Use (Bathing, Cleaning): Can tolerate higher levels of certain parameters (e.g., hardness, TDS) but must be free of pathogens and irritants.
Irrigation: Suitability is determined by parameters like salinity (TDS), sodium absorption ratio (SAR), and specific ion toxicity (e.g., Boron) that can affect soil permeability and crop health.
This practical utilizes rapid, colorimetric, and titrimetric methods provided in water testing kits to quantify these parameters. The results are then interpreted based on predefined standards to assign a suitable use for each sample, demonstrating applied environmental science.
Materials Required:
Water Testing Kit: (e.g., from Systronics, Lovibond, or a JAL-TARA type kit).
Water Samples: Collected from 3-4 different sources:
Sample A: Tap Water (Municipal Supply)
Sample B: Groundwater (Tube well/Borewell)
Sample C: Surface Water (River/Pond/Lake)
Sample D: Treated Wastewater (Optional)
Apparatus: Beakers (100 ml, 250 ml), measuring cylinder, glass rod, droppers, thermometer, stopwatch.
Distilled Water: For rinsing apparatus and as a blank.
Data Sheet: For recording observations.
Standards: Printout of BIS IS 10500:2012 (Drinking Water) and FAO Irrigation Water guidelines.
Procedure:
Step 1: Sample Collection and Labeling
Collect water samples in clean, sterile 1L plastic bottles.
Label each bottle clearly with the source, date, and time of collection.
Step 2: Testing of Parameters (Follow kit manual precisely)
For each sample (A, B, C, D), test the following parameters:
pH: Using pH strips or a digital pH meter.
Turbidity (NTU): Using a turbidity tube or meter.
Total Dissolved Solids (TDS): Using a TDS meter (in mg/L).
Total Hardness: By EDTA titration method (in mg/L as CaCO₃).
Chloride (Cl⁻): By Argentometric titration with Potassium Chromate indicator (in mg/L).
Nitrate (NO₃⁻): Colorimetric method using a reagent (in mg/L).
Free Chlorine Residual: (For tap water only) using DPD reagent (in mg/L).
Total Coliforms: Using a Presence/Absence test vial (incubate for 24-48 hours).
Step 3: Data Recording
Record all observations and calculated values in a structured table for each sample.
Step 4: Interpretation and Suitability Analysis
Compare the results for each sample against the standard permissible limits for different uses (Drinking, Domestic, Irrigation).
Assign a suitability category to each sample based on the most restrictive parameter it fails.
Observations & Data Analysis:
Table 1: Water Quality Analysis of Different Samples
| Parameter | Sample A: Tap Water | Sample B: Borewell Water | Sample C: Pond Water | Permissible Limit (Drinking) |
|---|---|---|---|---|
| pH | 7.2 | 7.8 | 8.2 | 6.5 - 8.5 |
| Turbidity (NTU) | 2 | 5 | 25 | 1 (5 Max) |
| TDS (mg/L) | 350 | 1800 | 450 | 500 (2000 Max) |
| Total Hardness (mg/L) | 200 | 600 | 250 | 200 (600 Max) |
| Chloride (mg/L) | 75 | 450 | 100 | 250 (1000 Max) |
| Nitrate (mg/L) | 10 | 25 | 40 | 45 |
| Free Cl₂ Residual (mg/L) | 0.4 | 0 | 0 | 0.2 - 1 |
| Coliform Bacteria | Absent | Present | Present | Absent/100ml |
Table 2: Suitability Analysis Based on Results
| Water Sample | Drinking | Domestic Use | Irrigation | Reason for Unsuitability |
|---|---|---|---|---|
| A: Tap Water | Suitable | Suitable | Suitable | Meets all BIS standards. |
| B: Borewell Water | Not Suitable | Not Suitable | Use with Caution | High TDS (Salinity), High Hardness, Fecal Contamination. |
| C: Pond Water | Not Suitable | Not Suitable | Suitable | High Turbidity, Fecal Contamination. |
Irrigation Suitability Note for Sample B:
TDS = 1800 mg/L places it in the "High Salinity Hazard" category per FAO guidelines. It can be used to irrigate salt-tolerant crops (e.g., barley) in well-drained soils with careful management to prevent soil salinization.
Result:
The analysis of the three water samples revealed significant differences in quality:
Sample A (Tap Water) was found to be suitable for drinking and all domestic purposes, complying with BIS IS 10500 standards.
Sample B (Borewell Water) was unsuitable for drinking and domestic use due to high salinity (TDS) and the presence of coliform bacteria. It could be used for irrigation only with strict precautions.
Sample C (Pond Water) was unsuitable for drinking and domestic use due to high turbidity and microbial contamination. However, it was suitable for irrigation after allowing suspended solids to settle.
Discussion:
Link to Health and Syllabus: The presence of coliforms in Samples B and C indicates fecal contamination and a potential risk of waterborne diseases like cholera, typhoid, and dysentery. This directly relates to the syllabus topic of "Impacts on environment, human health, and welfare."
Environmental Implications: High nitrate (40 mg/L) in the pond water suggests contamination from agricultural runoff or sewage, which can cause eutrophication and methemoglobinemia in infants. High TDS in the borewell water indicates geological leaching or pollution, rendering it unfit for consumption and damaging to plumbing.
Treatment Needs: The results dictate the level of treatment required:
Sample B requires reverse osmosis (RO) or distillation to reduce TDS, followed by disinfection.
Sample C requires simple sedimentation (to reduce turbidity) followed by vigorous disinfection (e.g., chlorination, UV) to make it safe for domestic use.
Limitations of Rapid Kits: While excellent for field screening, these kits provide semi-quantitative results. Confirmatory testing through sophisticated instruments (like AAS for metals) is needed for a complete assessment, especially for drinking water designation.
Water Justice: Access to clean water (Sample A) is a fundamental aspect of environmental justice. The variability in water quality highlights disparities that can exist between different communities, even within the same region.
Conclusion:
This practical successfully demonstrated the use of rapid water testing kits as an effective tool for the preliminary assessment of water quality and its suitability for various purposes. The experiment highlighted that water sources that appear clean can be chemically or microbiologically contaminated. Therefore, scientific assessment is non-negotiable for determining safe use. The ability to quickly evaluate water quality is a critical skill for environmental management, public health protection, and sustainable water resource planning, ensuring that water is used appropriately and safely according to its quality.
Viva Voce Questions:
Why is the presence of coliform bacteria a definitive indicator that water is unfit for drinking?
Coliforms themselves may not always cause illness, but they are a reliable indicator organism. Their presence signals that fecal contamination has occurred and that pathogens (disease-causing bacteria, viruses, protozoa) could be present, making the water unsafe to drink.
What is the significance of measuring "free chlorine residual" in tap water?
It indicates that a sufficient dose of chlorine was added at the treatment plant to disinfect the water and that a small amount remains to protect against re-contamination within the distribution pipeline. Its presence (0.2-1 mg/L) is a key sign of safely treated municipal water.
Sample B had high TDS and hardness. What is the difference between these two parameters?
TDS measures the total amount of mobile charged ions (both organic and inorganic) dissolved in water. Hardness is a specific measure of the concentration of divalent cations, primarily calcium (Ca²⁺) and magnesium (Mg²⁺) ions. All hardness contributes to TDS, but not all TDS is hardness (e.g., NaCl adds to TDS but not hardness).
Why is turbidity an important parameter, even if the water is chemically safe?
High turbidity reduces the effectiveness of disinfection. Pathogens can "hide" within suspended particles, shielding them from chlorine or UV light. It also makes water aesthetically unappealing and can indicate ongoing erosion or pollution.
Based on your results, what is the simplest way to improve Sample C (Pond Water) for domestic use like cleaning and bathing?
Simple sedimentation and filtration. Allowing the water to stand in a tank or using a cloth filter can significantly reduce turbidity by allowing suspended particles to settle out. This would make it acceptable for non-potable domestic uses, though disinfection would still be needed for it to be completely safe.
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