Water treatment basics: Which method effectively removes both temporary (carbonate) and permanent (non-carbonate) hardness from water in a single step?

Introduction:
Hardness in water arises from calcium and magnesium salts. Temporary hardness is mainly due to bicarbonates and can be reduced by boiling, while permanent hardness arises from chlorides, sulfates, and nitrates. Selecting a treatment that removes both forms is important for laboratory and certain process waters.

Given Data / Assumptions:

• Temporary hardness is removable by precipitation of carbonates upon boiling.
• Permanent hardness requires ion exchange, chemical softening, or phase-change methods.
• We need a single-step method that removes both types effectively.

Concept / Approach:
Distillation vaporizes water and condenses pure steam, leaving nonvolatile dissolved salts behind, thereby removing both temporary and permanent hardness in one operation. While ion exchange can also remove both hardness types, simple filtration or decantation cannot, and boiling alone addresses primarily temporary hardness.

Step-by-Step Solution:
Identify methods that physically separate water from dissolved ions: distillation qualifies.Exclude partial methods: boiling addresses temporary hardness only.Exclude mechanical separation methods: filtration/decantation do not remove dissolved ions.Select “distillation” as the comprehensive single-step solution listed.

Verification / Alternative check:
Laboratory-grade water production lines rely on distillation or reverse osmosis plus polishing resins to remove dissolved hardness completely.

Why Other Options Are Wrong:

• Boiling: Precipitates carbonates (temporary hardness) but leaves permanent hardness.
• Filtration/decantation: Do not remove dissolved ions.
• Ion exchange softening only: Effective, but not provided as the correct comprehensive option here compared with distillation.

Common Pitfalls:
Assuming any thermal treatment removes all ions; only vapor–condensation (distillation) achieves near-complete nonvolatile salt removal in one step.

Final Answer:
distillation