Treatment process
Distillation
Boiling water and condensing the vapour. The oldest purification method and among the most complete, but energy intensive enough that it is rarely the right answer at scale.
Key facts
- Scale
- Municipal and household
- Treatment stage
- Phase change
How it works
Water is evaporated, leaving dissolved solids behind, and the vapour is condensed. Volatile compounds with boiling points near or below water’s will carry over unless a fractionating stage is used.
What it removes — and what it does not
| Row | Removes | Does not remove |
|---|---|---|
| 1 | Essentially all dissolved salts and metals | Volatile organic compounds, which distil over with the water |
| 2 | Bacteria, viruses and protozoa | Dissolved gases |
| 3 | Nitrate, fluoride, arsenic, lead | — |
| 4 | Most PFAS | — |
Trade-offs
- Very high energy demand — roughly 2,260 kJ per kilogram for the latent heat alone
- Slow
- Product water is flat-tasting and demineralised
- Multi-stage flash and multi-effect distillation reuse the latent heat, which is what makes thermal desalination viable in energy-rich regions
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Sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- NSF International / American National Standards Institute — NSF/ANSI drinking water treatment unit standards. Public but restricted · Publisher terms — public access, reuse not clearly granted
- American Water Works Association — AWWA standards, water audits and utility benchmarking. Public but restricted · Publisher terms — public access, reuse not clearly granted