Clean and Polluted Water

Types of Bottled Water:
- Spring Water: Sourced from an underground formation from which water flows naturally to the surface of the earth.
- Well Water: Sourced from a hole bored, drilled, or otherwise constructed in the ground which taps the water of an aquifer.
- Distilled Water: Purified through distillation, a process where water is boiled into vapor and condensed back into liquid in a clean container, leaving behind solid contaminants and minerals.
- Mineral Water: Contains a constant level and relative proportions of mineral and trace elements at the point of emergence from the source.
Comparison of Bottled Water and Tap Water:
- Regulation: In Canada, tap water is regulated by municipal and provincial governments under strict guidelines (e.g., Guidelines for Canadian Drinking Water Quality), whereas bottled water is often regulated as a food product by the CFIA.
- Tap Water Benefits:
- Contains controlled levels of fluoride to prevent tooth decay.
- Undergoes rigorous testing for chlorine residuals to ensure ongoing disinfection throughout the piping system.
- Environmental Impact: Bottled water generates significant plastic waste and has a much higher carbon footprint due to transportation compared to local tap water.

Definition and Characteristics:
- Hard water contains high concentrations of multivalent cations, primarily calcium ( $Ca^{2+}$ ) and magnesium ( $Mg^{2+}$ ).
- Temporary Hardness: Caused by dissolved bicarbonate minerals (calcium bicarbonate and magnesium bicarbonate). This can be reduced by boiling.
- Permanent Hardness: Caused by sulfates or chlorides of calcium and magnesium, which cannot be removed by boiling.
Effects and Nuisances:
- Scale Build-up: When heated, calcium carbonate precipitates out, creating "limescale" in boilers, kettles, and pipes, reducing efficiency and lifespan.
- Chemical Reaction with Soap: The cations react with soap to form an insoluble precipitate known as "soap scum":
- $2C<em>{17}H</em>{35}COO^-Na^+ + Ca^{2+} \rightarrow (C<em>{17}H</em>{35}COO)_2Ca (s) + 2Na^+$
- Personal Care: Hard water can strip natural oils from skin and hair, potentially exacerbating conditions like eczema.

Ion Exchange Process:
- Most home softeners use an ion-exchange resin beads coated with sodium ( $Na^+$ ) or potassium ( $K^+$ ) ions.
- As hard water passes through, the resin captures $Ca^{2+}$ and $Mg^{2+}$ and releases $Na^+$ into the water.
- Regeneration: Periodically, the resin must be "recharged" with a concentrated brine solution (sodium chloride) to flush out the captured minerals.

Solubility Factors:
- Temperature: Cold water can hold more dissolved oxygen than warm water. Thermal pollution (from power plants) can lower DO levels dangerously.
- Atmospheric Pressure: Higher pressure increases gas solubility in water.
Biochemical Oxygen Demand (BOD):
- This measures the amount of oxygen required by aerobic microorganisms to decompose organic matter. High BOD indicates high levels of organic pollution.
- Eutrophication: Excessive nutrients (phosphorus and nitrogen) lead to algal blooms. When algae die, bacteria decompose them, consuming all available DO and creating "dead zones."

Physical Contaminants:
- Includes Macro-debris (plastic bottles, glass) and Micro-plastics (particles smaller than $5mm$ ).
- Suspended Solids: Fine particles like silt and clay that increase turbidity (cloudiness), blocking sunlight for aquatic plants.
Biological Contaminants:
- Pathogens: Bacteria (Salmonella, Cholera), Viruses (Hepatitis A, Norovirus), and Protozoa (Giardia lamblia, Cryptosporidium).
- Indicators: E. coli is used as an "indicator organism"; its presence suggests fecal contamination and the potential presence of other pathogens.
Chemical Contaminants:
- Inorganic: Heavy metals like Lead ( $Pb$ ), Mercury ( $Hg$ ), and Arsenic ( $As$ ) which bioaccumulate in the food chain.
- Organic: Volatile Organic Compounds (VOCs) such as benzene, pesticides (DDT), and Persistent Organic Pollutants (POPs) that do not break down easily in the environment.

Unconfined Aquifers: Have a permeable layer above them, making them highly susceptible to surface contamination from spills or agricultural runoff.
Confined Aquifers: Protected by an impermeable layer (aquitard or aquiclude) like clay. These are often under pressure; if a well is drilled into one, it may form an Artesian Well where water rises without pumping.