Drinking Water in Times of Disaster – Treating Water from Upland Catchment - A Practical Approach

Hutt River is the main source of water for Wellington. Base flows are stable throughout the year. Currently Hutt River water is extracted treated and supplied to consumers. Other streams in Wellington Green Belt are not used for drinking water supply. These streams have seasonal variations in quantity and quality. Wellington has earthquakes. Pipes may rupture and electric power may not be available to operate Hutt River water treatment plants or to boil water at homes. River & streams could be a direct water source. Issue would be treatment process.

The stream waters are low in turbidity. They may have organics like humic acid, added to the rainwater runoff from the humus layer in wooded areas.

To remove the organics, best remedy is adding activated carbon. Burnt bread/rice or wood charcoal can be ground, making powder activated carbon (PAC). Streamwater in an empty plastic bottle, mixed with PAC and settled will remove organics.

Aluminium Sulphate (Alum) is used for removing suspended solids. 10g alum in 1L water makes a 10000 mg/L stock solution. Hutt River water was dosed with this alum and a Jar Test (simulation of drinking water treatment process) was carried out. 40 ppm (mg/L) was the optimum Alum dose. Dose may vary depending on the source water turbidity, but usually alum dose is in the range 10-40 ppm.

For disinfection, Bleach solution (Sodium Hypochlorite) of commercially available strength 150g/L was used. 5 mL of Bleach in 1 L of water makes 0.5% bleach stock. 4 mL of this dilute stock solution is needed to treat 1 L of water. Chlorine residuals (after dosing) were measured using a chlorine tester.

The volume of a plastic bottle cap is 4 mL. To get 40 ppm dose of alum, 1 bottle-cap full of 10mg/L alum stock solution is added to 1 L of water. Shaking well and allowing 15 minutes to settle, then decanting top water leaves the settled sediment out. For disinfection, add one bottle cap of 0.5% bleach solution to 1L of decanted water. This will ensure approximate 1 ppm (1 mg/L) chlorine residual. After a contact time of 30 minutes, the water is safe to drink.

Application is user friendly, with easy to measure unit of “bottle caps”. The cost template of the whole operation (for a population of 10,000) is made is available online for disaster relief agencies.