Properties and Classification of Water

Clear, transparent, tasteless, and odorless fluid.
Colorless in small amounts, appearing pale blue in deeper columns.
Freezes at 0°C and boils at 100°C under normal pressure.
Greatest density occurs at 4°C.
Excellent solvent, capable of dissolving nearly all substances, including solids, liquids, and gases.

Pure Water: Free from chemical poisons and infectious diseases; safe for human consumption.
Polluted Water: Undergoes changes in physical characteristics like color, odor, and turbidity due to contaminants.
Contaminated Water: Contains animal and human wastes, potential carriers of infectious diseases and chemical poisons (e.g., Pb²⁺, As₅⁺).

Rain Water:
- Purest type, akin to distilled water, may have dissolved gases (O₂, NH₃, N₂, CO₂).
- Can be acidic due to CO₂ and nitrous oxides, which can be removed by boiling.
- May contain inorganic constituents (e.g., NaCl from ocean spray) and H₂SO₄ from SO₂ oxidation.
- Soft water; free from Ca²⁺ and Mg²⁺, but may have micro-organisms from the air.
Surface Water:
- Includes rivers, canals, lakes, and ponds.
- Exposed to contamination from dust, soil, sewage, and waste.
- Contains dissolved solids, CO₂, and organic acids.
- Home to pathogenic bacteria.
Underground Water:
- Forms when surface water percolates through soil.
- Generally purer and less polluted due to filtration.
- Contains higher concentrations of dissolved Ca²⁺ and Mg²⁺, making it harder than surface water.
- More acidic due to increased CO₂ from organic decomposition, and can contain medicinal sulphur.

Potable Water: Must be clear, colorless, odorless, neutral, and free from chemical poisons and infectious diseases.
Irrigation Water: Should be soft to avoid damaging soil and fibers in the textile industry.
Industrial Water: Must be pure and free from chemical damage during use.
Pharmaceutical Water: Omits chemical poisons, must be pyrogen-free.

Representative samples should be collected in inert materials (e.g., boro-silicate glass, hard rubber).
For distribution systems, flush lines adequately before collection.
Collect samples from wells only after sufficient pumping.
For rivers or streams, samples should be taken from top to bottom, ideally at the center of the stream.