Undergraduate Thesis - Feasibility of Rainwater Harvesting in Paarden Island

Assumptions

The following assumptions have been made regarding the pricing model used for a rainwater harvesting system:

• It was assumed that a generic model could be used to estimate the cost of a rainwater harvesting system. This assumption would not be correct for real world applications since none of the erven are the same, each erf that is listed has a unique solution. As an example the amount of plumbing that will be required will vary from erf to erf due to the layout of the building, the location of the rainwater tanks in relation to the down pipes and the rainwater tanks in relation to the location of where the water will be used;

• It was assumed that the cost of the roof materials, gutters and down pipes would be included in the cost of construction of a building and thus was not considered in the costing of a rainwater harvesting system. For erven that have aging or inappropriate roofs and broken gutters this cost will need to be considered as an additional cost since the roofs and gutters will need to be replaced;

• It was assumed that all erven would be able to afford and accommodate the number of polypropylene rainwater tanks required to completely capture all the rainwater that was available to the erf. The rainwater tanks can be expensive especially when large polypropylene tanks are used thus the use of 10 kL tanks were used in place of the 15 kL and 20 kL tanks due to the cost of storage per litre increasing with the increasing size of the rainwater tank. Rainwater tanks also use up valuable factory floor space which could be an issue for certain erven;

• It was assumed that all roof areas had roof surfaces and down pipes that were clean, appropriate and well maintained. This is not the case for many building in Paarden Island which still have roof surface made from asbestos materials. The buildings with asbestos roofing will need to be replaced in future if rainwater harvesting was to be implemented. Several roofs in Paarden Island are also in a state of disrepair and will need to be fixed before being used to help capture rainwater. It was also observed that most of the older building in Paarden Island had roof surfaces covered in what appeared to be moss like organic matter growing on the roof surfaces. These roof surfaces will need to be cleaned properly before the rainwater harvesting system can be used.

• It was assumed that an inflation of 6.5% per annum would be acceptable in the calculation of future cost of equipment that requires replacement.

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Costing model for a rainwater harvesting system

The costs of a rainwater harvesting systems are priced according to 6 separate components. The total cost the 6 separate components are used to estimate the cost of implementing a rainwater harvesting system on a erf over a 10 year period. The results in table H-1 are then compared to the results in table I-7 to assess if it would be feasible to implement a rainwater harvesting system for that particular erf.  

 

Assessment of Rainwater Harvesting System Equipment Costs

The results of the cost of various components of the rainwater harvesting system can be seen in table H-4 with a summary table given in table 5-7 for non-potable rainwater harvesting systems and 5-8 for potable rainwater harvesting systems. Table 5-6 gives the breakdown of how each component was calculated and the cost of each component.

 

The total cost of the non-potable rainwater harvesting for Paarden Island is estimated to be about R 45 million to completely install and operate rainwater harvesting systems for 10 years. The cost of rainwater harvesting systems range from between R 42 000 to R 1.7 million. The cost of the rainwater tanks was the highest cost component for both the potable and non-potable rainwater harvesting systems. The rainwater tanks consisted of about 59 % of the cost for non-potable systems and 42% for potable water systems. On average the post treatment Ultra Violet and Cartridge Filtration System only consisted of 2.6% of the total costs but the maintenance requirement of these systems was estimated to be 31% of the total cost.

 

Table 6‑2: Component cost breakdown and pricing method

 

 

 

 

 

 

 

 

 

 

 

Table 6-3: Summary cost of non-potable rainwater harvesting systems

 

 

 

 

 

 

 

 

 

 

Table 6‑4: Summary cost of potable rainwater harvesting systems