Rainfall Harvesting System Feasibility Study for Non-potable Usage in irelan

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In Ireland, the abundance of water resources is consequence of its high precipitation patterns, with an average annual rainfall of approximately 1230 mm [2]. The excessive rainfall results in one of the main problems of urban areas in Ireland, the flood. However, the water consumption per capita per day in Ireland is one of the highest in Europe, besides, with the rapid growth of the population, the demand for freshwater has increased and this means too much money being spent in water treatment.

The solution for the water issue in Ireland can be the water itself. The use of rainwater harvesting can convert the threat into opportunity, in other words, the adoption of this system in a large scale could prevent urban areas from flooding and recycle the water. However, it is necessary some stimulus from authorities so this solution could truly be implemented all over the island and the flood problem could be tackled.

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Irish Water Legislation

The history of Irish water legislation began in 1978, when Fianna Fáil (political party in the Republic of Ireland) abolished water charges. Since then, politicians had constantly changed the water charges system, creating controversy among the Irish population.

The recent event of this history, which brought anger in the Republic of Ireland, is when the Irish Water was incorporated as a semi-state company under the Water Services Act 2013 [4].

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Building a Rainfall Harvesting System

There are several techniques currently used for collecting and storing rainfall, which can vary in complexity according to the resources available for this and the demand for water in each location. Although there are three major forms of collecting rainwater, which are: in situ rainwater harvesting, external water harvesting and domestic rainwater harvesting. In this study, the focus will be on the domestic rainwater harvesting systems.

According to (Ling and Benham, 2014), there are six basic components of a rainwater harvesting system [5]:

- Catchment surface (Figure1): The rain is collected in a surface (e.g. roof). The amount of rainwater collected is a function of the type of material covering the surface and its area. The catchment material can also bias the quality of the water to be stored by contaminating it.

[pic 1]

Figure 1: Example of a catchment surface - rooftop catchment system. Source: http://www.gdrc.org/uem/water/rainwater/introduction.html

- Gutters and downspouts: These devices are used to collect and divert the water after it reaches the catchment surface (e.g. roof).

- Screens, first-flush diverters and roof washers (Figure 2): As the catchment surface is open air, these devices must be used in order to prevent the water contamination and to avoid clogging the system. The screens retain the solids such as leaves and some particulate materials, the first-flush is to cut off the first flush of a rain event and the roof washers consists of a tank with a strainer so it also improves the quality of the water.

[pic 2]

Figure 2: Example of a roof washer system and its devices. Source: http://www.solarhaven.org/WaterStorage.htm

- Cisterns (Figure 3): the cisterns consists on storage tanks to store the rainwater for further use. This part of the system is the most expensive one, which is because it must be constructed with the adequate materials in order to avoid contamination, prevent mosquitos to have access to surface water and algal growth due to insulation. The cistern capacity should be calculated according to dry spells duration, the amount of rainfall and the water consumption in the building.

[pic 3]

Figure 3: Design of a typical cistern. Source: https://optirtc.com/projects

- Delivery system: this system is required to convey the rainwater collected by the catchment surface to the cistern. Depending on the location of the cisterns, it may be necessary the use of a pump or a pressure tank.

- Treatment system: this is the last stage of the system and depends on the final use of the water collected, which can be potable or non-potable.

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Rainfall Water Treatment and Reuse

Harvested water is mostly low polluted depending on the quality of the atmosphere and can be used for any purposes. The use of the water, which can be potable or non-potable, only depends on the treatment that it will receive previously.

For non-potable uses usually no treatment is necessary beyond the roof washers and first-flush diverters, some of the uses for non-potable use are flushing toilets, washing clothes, watering garden and washing outdoor areas.

For potable use, it is necessary to treat the water properly and disinfect it before using. First, the sediment removal must be done by using fine filters (5 to 3 micron) with the finer one being an activated charcoal filter. There are a lot of disinfection methods that can be used for this purpose, one recommended method is chlorination that consists of applying chlorine for the deactivation of microorganisms. Slow sand filtration is a cheap alternative to improve the bacteriological quality of the water as well. The rapid sand filter is suitable for removal of hazardous substances, as these substances are particle-bound [5].

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Current Use

The climate change led many countries around the world to adopt the rainfall harvesting system as an alternative to have access to water in a sustainable way. Furthermore, most of these countries are using incentive laws in order to spread the rainwater harvesting throughout their territory.

In the United Kingdom, for example, several states have rainwater harvesting requirements on new constructions, besides giving 100% first year capital allowances for those adopting the system.

In Ireland, the recent water charges are stirring the interest of the population in using new strategies to reduce their water consumption and, consequently, lowering their bills. Currently, there are not enough incentives from the government and despite the potential that Ireland have in rainwater harvesting, it is not applied as much