Table 7.
Halogen disinfection products and recommended doses for point-of-use disinfection.
| Iodination techniquesa | Add to 1 L or qt of water |
|
|---|---|---|
| Amount to achieve 4 mg·L−1 | Amount to achieve 8 mg·L−1 | |
| Iodine tabsb | 0.5 tab (or 1 tab in 2 L) | 1 tab |
| Tetraglycine hydroperiodide | ||
| Emergency drinking water germicidal tablet | ||
| Potable aqua | ||
| Globaline | ||
| 2% iodine solution (tincture) | 0.25 mL | 0.5 mL |
| 5 dropsc | 10 drops | |
| 10% povidone–iodine solutiond | 0.4 mL | 0.8 mL |
| 8 drops | 16 drops | |
| Saturated solution: iodine crystals in watere | 13 mL | 26 mL |
| Add to 1 L or qt of water |
||
| Chlorination techniquesf | Amount to achieve 2 mg·L−1 | Amount to achieve 5 mg·L−1 |
|
| ||
| Sodium hypochlorite (household bleach 5%) | 1 drop | 0.1 mL 2 drops |
| Sodium hypochlorite (household bleach 8.25%) | 1 drop (in 2 L) | 1 drop |
| 1% bleach (CDC-WHO Safe Water System)g | 4–5 drops | 8–10 drops |
| Calcium hypochloriteh (Redi Chlor [0.1-g tab]) | Cannot use in small quantities of water for low concentrations | 0.25 tab |
| NaDCCi (Aquatab, Kintab) | ¼ tab of 8.5 mg NaDCC (may be impractical) | ½ tab (8.5 mg NaDCC) |
| Chlorine plus flocculating agent (Chlor-Floc tablets or powder sachets, PUR) | Not practical for small volumes and low concentrations | ½ tablet/yields 5 mg·L−1j |
CDC, Centers for Disease Control and Prevention; WHO, World Health Organization; NaDCC, sodium dichloroisocyanurate.
World Health Organization recommends only for short-term emergency use.
Iodine tablets were developed by the military with the criteria that they will disinfect water, including Giardia, with a short contact (holding) time of 10 min since troops in the field may not wait longer. This high concentration is not necessary for field disinfection of clear water; it is preferable to target 4 mg·L−1 and wait longer. Additionally, the recommendation to use 8 mg·L−1 for cloudy water will result in poor taste, so it is recommended to clarify the water first.
Measure of a drop varies from 16 to 24 gtt·mL−1, standard 20 gtt·mL−1 is used here.
Povidone-iodine solutions release free iodine in levels adequate for disinfection, but scant data are available. (See text above)
A small amount of elemental iodine goes into solution (no significant iodide is present); the saturated solution is used to disinfect drinking water. Water can be added to the crystals hundreds of times before they are completely dissolved.
Can easily be adapted to large or small quantities of water. Simple field test kits or swimming pool test kits with color strips are widely available to ensure adequate residual chlorine. In usual situations, EPA recommends a target residual of 4 mg·L−1. For household use, CDC recommends less than 2 mg·L−1. Many of the recommended emergency doses exceed this threshold.128 For treatment of large volumes, see formula to calculate in Lantagne 2008.177
Safe Water System for long-term routine household point-of-use water disinfection recommends a hypochlorite dose of about 2 mg·L−1 in clear water and 4 mg·L−1 in slightly turbid water. This results in a low yet effective target residual concentration but requires testing in a particular water source to ensure sufficient residual.
Stable, concentrated (70%), dry source of hypochlorite that is used for chlorination of swimming pools. Multiple products are available in various size tablets or granular form. Best formulation for large quantities of water.
Available in different strengths to treat different volumes of water. Check packaging to determine proper dose.
Use full tablet or sachet in highly turbid water.