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Q105 (NDA-II/2025) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Applied everyday chemistry Answer Verified

Which one of the following is considered to be the purest source of water ?

Result
Your answer: —  Â·  Correct: D
Explanation

Rainwater is considered the purest form of water in nature [2]. This is because it is essentially a product of natural distillation; as water evaporates from the Earth's surface, it leaves behind dissolved salts and impurities, which then condense and fall as rain [2]. While all natural waters contain some dissolved mineral salts, rainwater has the lowest concentration of Total Dissolved Solids (TDS), averaging around 7 mg/l compared to 118 mg/l for river water and 34,400 mg/l for seawater. Although it can pick up atmospheric gases, dust, or pollutants as it falls, it remains significantly purer than surface sources like rivers or seas, which accumulate minerals and organic matter from the land [2]. Groundwater sources like wells also contain higher mineral content due to percolation through rocks [2].

Sources

  1. [2] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 12: Water (Oceans) > SALINITY OF OCEAN WATERS > p. 104
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