Undergraduate Thesis - Feasibility of Rainwater Harvesting in Paarden Island

Estimated average monthly water consumption for erven in Paarden Island

The total cumulative average monthly water consumption for Paarden Island was estimated to be 41 000 kL which equates to 492 000 kL per annum. The average monthly water consumption for erven in Paarden Island was estimated to be 163 kL with an average standard deviation of 67 kL. The maximum average monthly water consumption was estimated to be 5 950 kL

 

Sizing of rainwater tanks

The results of the monthly surplus or deficient resulted in 3 different scenarios:

1. Scenario 1 was a result in which there was a rainwater surplus in every month of the year. In scenario 1 the tank size was estimate to be the equivalent of 2 months’ supply of the average monthly municipal water consumption. 10 erven were able to achieve this outcome;

2. Scenario 2 was the result in which there was a rainwater deficit in every month of the year. In scenario 2 the tank size was estimated to be the equivalent of the month with the highest rainwater collection volume. 96 erven achieved this outcome; and

3. Scenario 3 was the result in which there was a mixture of rainwater deficits and surpluses for various months of the year. The cumulative rainwater surpluses of the erven resulted in 2 outcomes. In outcome (a) the erven were able to achieve a partial freshwater supply for a certain number of moths. 57 erven achieved this outcome. In outcome (b) the erven were able to achieve a complete freshwater supply from the rainwater. 58 erven achieved this outcome.

 

Assessment of Rainwater Harvesting Equipment

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.

 

Cost of Municipal Water Substituted by Rainwater

The cost of municipal water that was substituted rainwater was calcuated using 3 pricing scenarios with 5 tariff models each. Scenario 3 can offer the highest benefit to erven. 

 

The Feasibility of Rainwater Harvesting Systems for Various Erven in Paarden Island

The number of erven that are able to make the implementation of rainwater harvesting in Paarden Island feasible increase as the tariff rate increases or the amount of rainwater that can be harvested and used is increased. Scenario 3 allows for the best outcome for the number of erven that can implement rainwater harvesting systems feasibly. Paarden Island would thus be able to implement non-potable rainwater harvesting systems in 34% to 72% of the current water account paying erven depending on the future municipal tariff rate increases. Paarden Island would be able to implement potable rainwater harvesting systems in 5% to 18% of the current water account paying erven depending on the future municipal tariff rate increases.