Chapter 3 · Water
Comparison table of methods
| Method | Parasites (Giardia, Crypto) | Bacteria | Viruses | Chemicals / salt | Notes |
|---|---|---|---|---|---|
| Boil 1 min (3 min >6,500 ft) | Yes | Yes | Yes | No | The most reliable. Requires fuel. |
| Unscented bleach | Giardia: partial. Crypto: no | Yes | Yes | No | Cheap. 30 min wait. |
| Iodine | Giardia: partial. Crypto: no | Yes | Yes | No | Not for pregnant women or people with thyroid problems. |
| Chlorine dioxide | Giardia: yes. Crypto: partial (respect the time) | Yes | Yes | No | Long waits; follow the label. |
| Filter ≤1 micron / NSF 53 or 58 | Yes | Not all | No | No | Combine it with disinfection. |
| Filter ≤0.3 microns | Yes | Yes | No | No | Combine it with disinfection. |
| Portable UV light | Yes | Yes | Yes | No | Clear water only; needs batteries. |
| SODIS | Reduces most germs, no guarantee | No | Last resort; 6 h to 2 days. | ||
| Distillation | Yes | Yes | Yes | Salt and metals: yes | Slow; the only method for seawater. |
| Filter + disinfect | Yes | Yes | Yes | No | The best practical option in the field. |
Source of the ratings: CDC, water treatment guidance for remote areas. "Partial" ratings mean the method is not reliable on its own against that germ.
