Use of water in daily life & related functions

Overview & Fundamental Concept

Complete preparation guide for Use of water in daily life & related functions under AISSEE Class VI General Knowledge (Syllabus Item 14). Master high-yield facts, exam matrices, solved models, and 10 interactive drill MCQs with detailed explanations.

• Biological Significance of Water: Liquid water is the universal biochemical solvent; constitutes approximately 65% of the average human body weight (up to 75% in infants); blood plasma consists of 90% to 92% water; essential for cellular cytoplasm structure, enzymatic digestion, waste filtration via kidneys (urine), and evaporative thermoregulation via sweat.
• Human Daily Intake: A healthy child requires approximately 1.5 to 2 liters of water daily, while an adult requires 2.5 to 3 liters (8 to 10 standard glasses) to maintain homeostatic fluid balance and prevent cellular dehydration.
• Global & Domestic Water Partitioning: Agriculture accounts for ~70% of total freshwater withdrawal (crop irrigation); industrial manufacturing and thermoelectric cooling consume ~20%; domestic residential use accounts for ~10%.
• The Groundwater Table: The subterranean upper boundary below which all pore spaces and rock fissures are saturated with water (phreatic zone); recharged naturally by rainfall percolation and infiltration.
• Aquifer Depletion Drivers: Excessive unmetered submersible bore-well pumping for high water-consuming cash crops (paddy, sugarcane), extensive urban concretization obstructing soil rainwater absorption, and erratic monsoon seasons.

• Archimedes' Buoyancy Principle: When an object is wholly or partially immersed in a fluid, it experiences an upward buoyant force equal to the weight of the fluid displaced by the object.
• The Governing Law of Flotation: An object FLOATS if its average density is LESS than the density of the surrounding liquid; an object SINKS if its average density is GREATER than the density of the liquid.
• The Iron Nail vs Giant Iron Ship Paradox (NCERT Class 5 EVS): A solid iron nail has a high density (~7.8 g/cm³) exceeding that of water (1.0 g/cm³); it displaces only a tiny droplet volume of water whose buoyant upthrust is negligible compared to the nail's weight, causing it to sink to the bottom; A massive ship constructed of heavy steel plates is hollowed out with immense air cavities inside, reducing its aggregate average density to far less than seawater; it displaces an enormous volume of water whose buoyant force effortlessly balances the ship's massive weight!
• Everyday Sinking vs Floating Observations (NCERT Chapter 7): • A solid soap bar sinks instantly in a tub of water, but if placed gently upon a wide plastic soap-case, both the soap and case float together! • A flat unpuffed disk of wheat dough sinks to the bottom of hot oil; when puffed into a hollow balloon-like puri filled with hot steam, its average density plummets, causing the puri to pop up and float on the oil! • A flat sheet of aluminum foil floats on water; when rolled into a tight compact ball, it sinks! • An empty plastic bottle floats with its cap closed; when filled completely with water, it submerges and sinks.

• The Salt Water Density Experiment (NCERT Class 5 EVS): When an egg or fresh lemon is dropped into a glass of plain tap water, it sinks directly to the bottom because the egg/lemon's density is greater than freshwater (1.0 g/cm³); as common salt (NaCl) is progressively dissolved into the water, the water's density steadily increases; when enough salt is added, the brine's density surpasses that of the lemon/egg, causing it to rise and float on the surface!
• The Dead Sea (The Saltiest Water Body): Located in the Jordan Rift Valley between Jordan and Israel/Palestine; shoreline sits at ~430 meters below sea level (Earth's lowest land elevation); contains approximately 300 grams of dissolved salt per 1 liter of water (salinity 30% to 34%, roughly 9 to 10 times saltier than regular oceans).
• Flotation in the Dead Sea: Because of its extraordinary salinity and high liquid density (~1.24 g/cm³), the human body (density ~0.985 g/cm³) is substantially lighter than Dead Sea water; a person CANNOT drown in the Dead Sea — swimmers float effortlessly on the surface like a piece of cork, reading books without treading water!
• The Dandi March (Salt Satyagraha - 1930): In British colonial India, the British government imposed a heavy salt tax and outlawed the collection or sale of sea salt; Mahatma Gandhi recognized salt as a universal, non-negotiable daily necessity for every rich and poor person alike; on March 12, 1930, Gandhi with 78 volunteers began a 24-day, 240-mile (386 km) march on foot from Sabarmati Ashram (Ahmedabad) to the coastal village of Dandi (Navsari, Gujarat); on April 6, 1930, Gandhi picked up a handful of natural salt from the beach, defying the British salt laws and launching the Civil Disobedience Movement.

• Potable Water Standards: Water that is crystal clear, colorless, odorless, free of toxic heavy metals, and microbiologically pure (zero pathogenic bacteria, viruses, or parasites) suitable for human consumption.
• 1. Boiling: The gold-standard physical thermal disinfection method; boiling water vigorously at 100°C for at least 10 to 15 minutes denatures microbial proteins, destroying 100% of pathogenic bacteria, amoebic cysts, and viruses.
• 2. Alum (Phitkari - Potassium Aluminum Sulfate) Coagulation: Swirling an alum crystal in turbid water releases trivalent aluminum ions ($Al^{3+}$) that neutralize the negative electrostatic charges on suspended clay and silt particles; particles clump into heavy aggregates called 'flocs' that rapidly settle to the bottom (accelerated sedimentation), allowing clean water to be decanted.
• 3. Chemical Chlorination: Adding measured chlorine tablets, liquid sodium hypochlorite, or bleaching powder (Calcium Oxychloride - $\text{CaOCl}_2$) to water; releases hypochlorous acid (HOCl) which penetrates bacterial membranes and destroys cellular metabolic enzymes.
• 4. Reverse Osmosis (RO): Applied hydraulic pressure forces water through a synthetic semi-permeable membrane with microscopic pores (0.0001 microns); blocks dissolved mineral salts (TDS), pesticides, fluoride, arsenic, and nitrates, allowing only pure water molecules to pass.
• 5. Ultraviolet (UV) Treatment: Exposes flowing water to germicidal UV-C light (wavelength ~254 nm); alters the thymine dimers in microbial DNA, rendering bacteria and viruses sterile and incapable of reproduction.
• Water Contamination Diseases: Ingesting contaminated unboiled water transmits Cholera (Vibrio cholerae), Typhoid (Salmonella typhi), Dysentery (Shigella / Entamoeba histolytica), Hepatitis A (Jaundice virus), and Polio; Oral Rehydration Salts (ORS) solution (clean boiled water + salt + sugar) is the vital first-aid treatment for severe dehydration caused by diarrhea.