3. inactivation the use of chlorine, ultraviolet light or other methods to disinfect the – water. All principles help to make drinking-water free of pathogens. Examples The following worked examples indicate some of the solutions that may be available in making decisions about treatment options. They do not constitute a complete list, nor will they be appropriate in every situation. In most cases, water testing and a pilot are needed to make sure that local conditions are suitable for a particular treatment method. Part of the process of considering treatment options is to calculate the costs of the alternatives. Develop the costings for your particular plant using up-to-date and local costs. An important element to include is the effect of the long-term operating costs. Sometimes an option that looks cheap initially can cost a lot more in the long term. 10.1 Scenario 1: Shorthop Community Hall Community: A community hall uses up to 2000 litres per day. There may be little or no water use for many days at a time. Water source: Rainwater is taken from a roof catchment and stored in a 20,000-litre tank (Figure 15). Existing treatment: None Water quality issues: There is no chemical contamination, but water quality testing is finding faecal coliforms in the water. The roof is the source of the contamination. Figure 15: Existing water supply system at Shorthop Community Hall Option 1: Add a second storage tank Trimming overhanging branches around the building reduce the tendency for birds to rest above the rooftop and would prevent access by possums. This measure therefore minimises source contamination. A screen on the gutter outlet is useful to divert debris such as leaves (Figure 16). Self cleaning designs are available. When it rains, the first flush of water from the roof may contain most of the pathogens from bird and animal droppings and other debris. It may also contain sediments, waterborne heavy metals and chemical residues that have collected on the
3. inactivation – the use of chlorine, ultraviolet light or other methods to disinfect the water. All principles help to make drinking-water free of pathogens. Examples The following worked examples indicate some of the solutions that may be available in making decisions about treatment options. They do not constitute a complete list, nor will they be appropriate in every situation. In most cases, water testing and a pilot are needed to make sure that local conditions are suitable for a particular treatment method. Part of the process of considering treatment options is to calculate the costs of the alternatives. Develop the costings for your particular plant using up-to-date and local costs. An important element to include is the effect of the long-term operating costs. Sometimes an option that looks cheap initially can cost a lot more in the long term. 10.1 Scenario 1: Shorthop Community Hall Community: A community hall uses up to 2000 litres per day. There may be little or no water use for many days at a time. Water source: Rainwater is taken from a roof catchment and stored in a 20,000-litre tank (Figure 15). Existing treatment: None Water quality issues: There is no chemical contamination, but water quality testing is finding faecal coliforms in the water. The roof is the source of the contamination. Figure 15: Existing water supply system at Shorthop Community Hall Option 1: Add a second storage tank Trimming overhanging branches around the building reduce the tendency for birds to rest above the rooftop and would prevent access by possums. This measure therefore minimises source contamination. A screen on the gutter outlet is useful to divert debris such as leaves (Figure 16). Self cleaning designs are available. When it rains, the first flush of water from the roof may contain most of the pathogens from bird and animal droppings and other debris. It may also contain sediments, waterborne heavy metals and chemical residues that have collected on the
treatment-options-small-drinking-water-supplies-jan14.docx