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“What is the most significant factor in determining whether water is safe…

- - - - Heavy metals
        
        Often leach from old household plumbing, mining runoff, or natural mineral deposits in groundwater. Common examples include Lead, Arsenic, Copper, Chromium, and Mercury
      - Agricultural Chemicals
        
        Fertilisers, herbicides, and insecticides can seep into both surface water and groundwater. Nitrates and Atrazine are common examples
      - How can water become contaminated?
        
        Heavy rainfall can wash animal manure from farms or untreated urban runoff into rivers, reservoirs, and shallow wells.
        
        Malfunctioning septic systems, leaking latrines, and sewage overflows can directly discharge pathogens into groundwater or surface water.
        
        Aging pipelines and pressure drops in city water networks can cause contaminated groundwater to seep into cracks or result in bacterial growth within the pipes.
    - - Microbial contamination in water refers to the presence of harmful microorganisms such as bacteria, viruses, protozoa, and fungi, capable of causing illness if consumed
        
        Common microorganisms that can be found as a contaminant in water include bacteria such as E. coli, Salmonella, Vibrio cholerae, and Shigella
        
        The presence of E. coli in water means there are living bacterial cells made of organic molecules, which can be detected through colour-changing reactions or nutrient agar tests that respond to E. coli’s metabolic activity. This indicates the water may be contaminated with faecal matter and unsafe to drink.
        
        The risk of sudden and serious health problems mostly comes from microbial contamination. It is the main reason authorities issue boil water alerts or advice not to drink water from taps in rare incidents.
        
        This unpredictability means identifying microbial contamination is a very significant factor when determining if water is safe to drink
        
        Contamination almost always stems from human or animal fecal matter entering water sources
- - - - Test Strips & Reagent Drops: Paper strips or chemical drops are added to a water sample. They rely on colorimetric reactions where a color change indicates the presence and concentration of specific chemicals like chlorine, pH, nitrates, and water hardness.
        
        pH testing strips:
      - Electrochemical Probes: Handheld meters use digital sensors to measure parameters such as pH, dissolved oxygen (O2), conductivity, and Total Dissolved Solids (TDS)
        
        Electrochemical Probes:
      - Using agar plates to test water contamination involves spreading water samples over a nutrient-rich gel to encourage microbial growth. If bacteria or fungi are present, they will multiply into visible, distinct colonies after incubation.
        
        Agar plate with visible E.coli colony
    - - Chromatography separates a water sample into its individual chemical parts by passing it through a system where different compounds travel at different speeds. This allows scientists to identify and measure trace pollutants, like heavy metals or pesticides
        
        Paper chromatography:
      - Mass spectrometry (MS) tests water cleanliness by vaporizing a water sample and ionizing its molecules to measure their exact mass-to-charge ratio
        
        How mass spectrometry works:
- - - - water that is too acidic or alkaline can corrode pipes, which causes harmful metals to leech (the process where a liquid solvent {usually water} dissolves and washes away soluble substances or minerals from a solid material)
    - - Excessive levels of calcium and magnesium determine water "hardness" measured as Total Dissolved Solids (TDS)
    - - Disinfectant chemicals like chlorine or chloramine can react with organic matter to form disinfection by-products or DBPs
    - - High levels of Nitrate are often result from agricultural runoff
- - - - Amphoteric means a substance can act as both an acid and a base. Water (H2O) is amphoteric because it can either donate a proton (H+) or accept a proton, depending on the other substances present in the chemical reaction.
    - - Due to its molecular structure, water is highly polar, with a partial positive charge on the hydrogen atoms and a partial negative charge on the oxygen atom. This polarity makes it an excellent solvent for polar and ionic substances.
    - - Pure water undergoes self-ionisation (or autoionization), where a small fraction of water molecules break apart into positively charged hydronium ions (H3O+) and negatively charged hydroxide ions (OH-)
    - - Water reacts with metal oxides and metal halides, a process known as hydrolysis. For instance, it can break down compounds like metal hydrides and carbides and reacts violently with alkali metals (like sodium or potassium) to produce metal hydroxides and hydrogen gas.
    - - Water is considered neutral, with a pH of 7 at 25 °C. This is because the concentrations of H3O+ and OH- ions in pure water are equal, as shown by studies from the Drinking Water Inspectorate.