Ensuring the safety and purity of water supplies is a fundamental requirement for public health and environmental protection. The examination of water, also known as water analysis, follows systematic procedures to identify water quality and detect the presence of impurities. These tests serve several critical purposes: determining the quality of water and the quantity of various impurities, verifying whether treated water meets required standards, identifying the appropriate dosage of treatment chemicals such as chlorine and coagulants, and prescribing the degree of treatment needed for the desired water quality. Understanding these methods is essential for engineers, public health officials, and anyone concerned with drinking water quality standards. This article explores the three main categories of water testing: physical, chemical, and biological examination.
Sampling Techniques for Reliable Water Analysis
Before any laboratory testing begins, proper sample collection is essential. A poorly collected sample can render even the most sophisticated analysis meaningless. The following guidelines ensure that water samples accurately represent the water source being tested:
- Fully cleaned bottles, buckets, or jerricans should be used for physical tests, with containers having a capacity greater than 2 liters for biological and chemical tests
- Containers must be rinsed thoroughly before sampling to avoid contamination from previous contents
- Samples should be well shaken before testing to ensure uniform distribution of any suspended particles
- When collecting from distribution lines, taps should be left open for two to three minutes to flush out stagnant water
- For well water with a hand pump, pump water for about 5 minutes before collecting into a clean, sterilized container
- When sampling from rivers, reservoirs, or lakes, collect water from 40 to 50 cm below the surface, avoiding locations too far from or too near the draw-off site
- Microbiological samples should be tested within 1 hour of collection; if this is not possible, keep samples in an ice chest or cooler for up to 24 hours
These sampling protocols are just as important when assessing hard water quality assessment, where dissolved minerals can significantly affect both test results and subsequent treatment decisions.
Physical Examination of Water
The physical examination of water involves three primary parameters that can be observed and measured without extensive chemical reactions. These tests provide immediate insight into the general condition of a water sample.
Temperature
Water temperature is measured using ordinary thermometers. Surface water temperatures generally match atmospheric conditions, while groundwater may be slightly cooler or warmer. Temperature significantly affects other physical properties including density, viscosity, surface tension, the saturation value of dissolved gases, and biological activity. For public water supply, the ideal temperature range is between 10 and 15.6 degrees Celsius. Water above 25 degrees Celsius is considered undesirable, and anything above 35 degrees Celsius is unfit for public supply.
Colour
Pure water is colourless, but natural waters often contain foreign substances that impart colour. Water with colour caused by suspended matter is said to have apparent colour. Colour contributed by dissolved solids that remain after removing suspended matter is known as true colour. Organic compounds causing true colour can exert chlorine demand, seriously reducing the effectiveness of chlorine as a disinfectant. Colour intensity is measured on a platinum-cobalt scale using a tintometer. One unit equals one milligram of potassium plus half a milligram of metallic cobalt dissolved in one liter of distilled water. For drinking water, colour should not exceed 5 ppm on this scale, although values up to 25 ppm may be tolerated.
Turbidity
Turbidity measures the extent to which light is absorbed or scattered by suspended material in water. This is influenced by both the size and surface characteristics of suspended particles, so turbidity is not a direct quantitative measurement of suspended solids. For example, a single pebble in water produces virtually no turbidity, but if crushed into thousands of colloidal-size particles, measurable turbidity results. The original Jackson turbidity meter used a long tube and standardized candle, with one Jackson Turbidity Unit (JTU) equal to the turbidity produced by 1 mg of SiO2 in 1 liter of distilled water. Modern measurements use nephelometric turbidity units (NTU). A turbidity of 5 NTU is the acceptable limit for drinking water, while values exceeding 10 NTU are rejected.
These physical properties share similarities with principles used in financial examination standards, where standardized measurement protocols ensure consistent and comparable results across different testing scenarios.
Chemical Examination of Water
The chemical examination of water involves tests to determine chemical impurities and corresponding chemical characteristics. These analyses reveal the dissolved mineral content and chemical properties that affect water suitability for various uses.
Total Solids
Solids present in water may be either dissolved or suspended. The sum of these is the total solids content, generally expressed in parts per million (ppm) or milligrams per liter. The measurement procedure involves evaporating a water sample in an oven at 103 to 105 degrees Celsius for 24 hours. The residue obtained represents total solids. If this residue is further ignited in a muffle furnace at 600 degrees Celsius for 15 to 20 minutes, volatile solids escape, leaving only fixed or inorganic solids behind. This distinction between volatile and fixed solids helps identify whether contamination is organic or mineral in nature.
pH Value
pH is the symbol for the logarithm of the reciprocal of hydrogen ion concentration, used to express the acidity or alkalinity of a solution on a scale of 0 to 14. Values below 7 indicate acidity, 7 represents neutrality, and values above 7 indicate alkalinity. pH is determined using electrometric or colorimetric methods. The acceptable pH range for drinking water is 6.5 to 8.5. Water outside this range can cause corrosion in pipes, affect the effectiveness of disinfection, and produce undesirable taste. Understanding pH is also critical when designing hot water system design, as water chemistry directly impacts scaling and corrosion rates in heating equipment.
| Parameter | Acceptable Limit | Cause for Rejection | Measurement Method |
|---|---|---|---|
| Temperature | 10-15.6 degrees C | Above 25 degrees C | Thermometer |
| Colour | 5 ppm | Above 25 ppm | Tintometer (Pt-Co scale) |
| Turbidity | 5 NTU | Above 10 NTU | Nephelometer / Turbidity meter |
| pH | 6.5 to 8.5 | Below 6.5 or above 8.5 | Electrometric / Colorimetric |
| Total Solids | 500 ppm | Above 2000 ppm | Evaporation at 103-105 C |
Biological Examination of Water
Pathogenic bacteria are difficult to detect directly because they are present in small numbers, even in polluted water, and appear infrequently or at irregular intervals. Testing for all known pathogens would be extremely time-consuming and impractical. Instead, water purity is checked using indicator organisms whose presence suggests contamination has occurred. The most common indicator is Escherichia coli (E. coli), a non-pathogenic bacterium found in large quantities in the intestines of humans and animals. The absence of E. coli provides reasonable assurance that water is free from pathogens, since both harmful and harmless bacteria typically occur together.
Proper sampling and testing are essential for accurate biological analysis, much like accurate water supply system demand calculations are essential for designing distribution networks that deliver safe water to consumers.
Total Count or Standard Plate Count Test
In this method, 1 ml of a water sample is diluted in 99 ml of sterilized distilled water. The diluted sample is then mixed with 10 ml of agar gelatin, a culture medium used to cultivate bacteria, and incubated at 37 degrees Celsius for 24 hours or 48 hours at 20 degrees Celsius. The bacterial colonies that form are counted, and results are computed per 100 ml. For drinking water, the total count should not exceed 1 per 100 ml.
Multiple Tube Fermentation Technique
This comprehensive test is divided into three stages:
- Presumptive test based on the ability of coliform group bacteria to ferment lactose broth and produce gas. Definite amounts of diluted water samples (0.1 ml, 1.0 ml, 10 ml, etc.) are placed in standard fermentation tubes containing lactose broth and incubated at 37 degrees Celsius for 48 hours. Gas production indicates a positive result for the presence of the E. coli group.
- Confirmed test uses a portion of water from the presumptive test placed in another fermentation tube containing brilliant green lactose bile as a culture medium. This medium suppresses the growth of other organisms. After incubation at 37 degrees Celsius for 48 hours, gas evolution confirms the presence of coliform group organisms.
- Completed test involves taking colonies grown in the confirmed test and placing them in lactose broth fermentation tubes and agar tubes for incubation at 37 degrees Celsius for 24 to 48 hours. Gas production provides final confirmation of E. coli presence, after which further detailed tests identify the specific type of bacteria.
Membrane Filter Technique
This efficient method retains bacteria present in water on a membrane with microscopic pores. The membrane is then placed in contact with a suitable nutrient medium that inhibits the growth of bacteria other than coliform organisms. After incubation at 37 degrees Celsius for 20 hours, coliform group bacteria develop into visible colonies that can be counted with a microscope. The result is calculated as coliform colonies per 100 ml using the formula: (colony counted / ml of sample) x 100.
pH Measurement and Its Importance in Water Testing
Among the chemical parameters tested, pH deserves special attention because of its wide-ranging effects on water quality and treatment processes. Accurate pH determination methods include both electrometric techniques using pH meters and colorimetric methods using indicator solutions or test strips. The pH value influences coagulation and flocculation efficiency, disinfection effectiveness (particularly chlorine), corrosion rates in distribution systems, and the solubility of metals. Low pH water tends to be corrosive, dissolving metals from pipes, while high pH water can cause scaling and reduce the effectiveness of chlorination. Regular pH monitoring is therefore a routine but critical component of any water quality testing program.
Conclusion: The Importance of Comprehensive Water Examination
The examination of water through physical, chemical, and biological testing forms the foundation of modern water quality management. Physical tests provide immediate information about appearance and basic characteristics, chemical analysis reveals dissolved constituents that affect health and usability, and biological testing ensures microbiological safety by detecting indicator organisms. Together, these three categories of testing create a complete picture of water quality, from source to tap. For engineers and planners involved in water distribution management, understanding these testing methods is essential for designing treatment systems, monitoring performance, and ensuring that water meets regulatory standards. Regular and systematic water examination protects public health, extends the life of infrastructure, and provides the data needed for informed water resource management decisions.