Undergraduate Thesis - Feasibility of Rainwater Harvesting in Paarden Island

The benefits of rainwater harvesting

There is a wide range of benefits to using rainwater harvest systems. These benefits include (Krishna, 2003):

• Providing a free source of water where the only costs are those which the user paid for the system to be installed;

• The ability to provide a source of water when there is no other water source available;

• The recharge of groundwater supplies using techniques of soil infiltration;

• The ability to provide good quality water if the groundwater is contaminated or unacceptable;

• A method of replacing or complementing conventional water sources if their cost of supply is too high. This includes providing a good source of landscape irrigation, water for non-potable and potable indoor uses after the rainwater has undergone the appropriate treatment;

• The reduction of stormwater runoff which could lead to a reduced risk of flooding;

• The reduction of non-point source pollution;

• The reduction of erosion in urban areas

• The ability to provide water that is naturally soft which reduces the need for water softeners;

• The ability to provide water that has a neutral or slightly acidic pH;

• The ability to provide water that is sodium free for people on low sodium diets;

• Helping water utilities reduce the peak demand for water during the wet season as well as delaying the expansion of water treatment plants;

• Providing water for cooling, air-conditioning plants and fire protection systems;

• Reducing the demands on groundwater sources; and 

• Saving the user money in water utility bills.

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Additional benefits include (Texas Rainwater Harvesting Evaluation Committee, 2006):

• Reducing scale build-up in hot water heaters; and 

• The use of less soap or detergent is required due to the natural softness of the water. 

 

Rainwater harvesting systems are also able to provide water close to the point where it is used, thus reducing the need for long distance conveyance which is require by conventional water systems. Users of rainwater harvesting are also more likely to be water conscious and therefore conserve water more than conventional water users. (UNEP, 2002, p. 3)

 

Rainwater harvesting is also thought of as being “socially acceptable and environmentally responsible” (Khoury-Nolde, 2008, p. 7) in Europe. According to UN-HABITAT (2005, p. 3) the increase in ground water recharge could lead to raising the levels of wells and boreholes that were previously drying up. UN-HABITAT (2005, p. 3) also found rainwater harvesting could mitigate the effects of drought as well as being an ideal water source for areas that lacked or had inadequate access to other water sources. There would also be a saving of energy that would normally be required to lift ground water. Rainwater harvesting systems are also able to provide a decentralised water distribution system that will not be as vulnerable to natural disaster as a centralised system. Decentralised systems can also reduce urban water shortages and reduce pollution to natural rivers (Moglia, et al., 2011).

 

The disadvantages of rainwater harvesting

Even though rainwater harvesting has numerous advantages it also has disadvantages. According to UNEP (2002, p. 13) the disadvantages of rainwater harvesting and utilization systems include:

• The small catchment areas and storage volumes are not always able to cope with the variation of weather patterns. Thus in times of drought the storage tank can dry up;

• The maintenance of rainwater harvesting systems and quality of collected rainwater can be difficult for some users to comprehend;

• A reduction of income to public water systems due to large scale implementation of rainwater harvesting; 

• The lack of clear guidelines for users and developers to follow since rainwater harvesting systems are not usually part of the building codes;

• Not being recognized by the public sector as an alternative water supply and communities do not demand rainwater to be utilised in their communities;

• Storage tanks being hazardous to children who play around them;

• Storage tanks taking up valuable space; and

• The costs of large scale rainwater harvesting systems could also be too high if they are not shared with other systems as part of an integrated system.

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Khoury-Noulde (2008, p. 7) also considered other problems with rainwater harvesting systems which included:

• The sizing of the storage tank. If the tank is made too small then there will be wastage of rainwater and if the storage tank is made too large then the construction and operating costs will be much higher and the storage tank may never get filled;

• The risk of contamination from various animal wastes and other organic matter if the tank is not properly sealed. Contamination could result in health risks if the rainwater is not treated before it is used for consumption; and

• The risk of causing deterioration of load bearing slopes due to leakage from the storage tanks.

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Every engineered system that is designed and implemented has its own benefits and disadvantages, and in a world where good clean freshwater is becoming a “national and regional priority” (UN-HABITAT, 2005, p. 2)  new ways of collecting freshwater is sure to gain momentum. A UNEP report on Rainwater Harvesting and Utilisation (2002) pointed out that, members of society, politicians and engineers need to consider what the other alternatives are, what are their advantages and disadvantages and how does rainwater harvesting compare to these other alternatives.