Utilization of Rain Water as a Source of Fresh WaterfI

Fresh water is a very important requirement for human life. Fresh water source can be derived from groundwater, river water, sea water, rain water or from other sources. Fresh water is one of the main things needed to fulfill human life.

Drying up the sources of holy water (spring water) in the Bali becomes complicated talked, not only religious groups but also academics and the general public began to worry about this condition. The drying up of water sources is an indication that the island began to trouble to produce water, while the water in Bali is not only needed for daily activities but also for spiritual activities (religious). Sources of springs that exist in Bali most also be used as a source of holy water for religious activities. In addition to fresh water is also a major agricultural need in Bali. Subak which became agricultural organizations in Bali overwhelmed to even begin to consistently provide a source of water for agriculture. Obviously these conditions will increasingly urgent not only the existence of agriculture in Bali, but also the survival of the people in it. This drought has also been a talk of the Ministry of Environment (MOE). Since 1995, the Ministry of Environment predicts Bali will experience a water deficit of as much as 1 billion cubic meters / year and will continue to increase to approximately 27.6 billion cubic meters per year by 2015. Not only that, the Center for Sustainable Development Studies, University of Udayana also mentioned in 2015 Bali experienced a shortage of clean water to 1,500 liters per second.

According to the Directorate General of Human Settlements Department of Public Works standard clean water needs in Indonesia is 60 liters / person / day. Fresh water is a basic requirement of each individual, because of that, it is necessary to find alternative sources of fresh water from any other sources than groundwater or surface water. Although it is clearly mentioned in the regulations No. 14 of 2010 minister of public works on minimum standards need for clean water per capita, but in fact there are so many people who do not have access to it. Regional Water Company as the representative of the government is only able to provide access to clean water to residents in those urban areas. If the Regional Water Company is not able to provide access to clean water in certain communities, they are still able to gain access to clean water, for example from groundwater or surface water. However in some locations that are physically there are no good road access, drainage limitations, or even limited surface water and ground water, the local communities are really hard to get clean water. Natural and government are also equally difficult to provide access to clean water to them. It occurs in several locations in Bali that is commonly in the mountainous areas, such as above area of Kintamani, the region at the foot of Mount Agung Karangasem, and mountainous areas of Buleleng.

Limitations of existing water sources in particular location in Bali is inversely proportional to the amount of rainfall in these locations. The mountains area of Bali is precisely the location with the highest rainfall. This is then used as the primary source of fresh water in the mountainous region of Bali, not only for everyday needs but even for agricultural activities. Thus rain water can be used as a good alternative source of water obtained from springs, ground water and surface water given the availability of high rainfall. According to the Meteorology and Geophysics average rainfall in Bali reached 2112 mm per year. This shows that there is so much rain that falls to the ground and then flows into the sea and not utilized at all. That's why we need a method to utilize the rain water as one way to meet the water needs of the people in Bali.

How do catch the rain water?

According Maryono and Santoso (2006) rain harvesting effort is currently international attention on the global agenda Environmental Water Resources Management in the context of prevention of water imbalance in the rainy and dry season, lack of clean water supply of the world population, as well as flood prevention and drought. Rainwater harvesting technique is defined as a way of collecting rainwater or surface runoff during heavy rainfall for the next use water during low rainfall.

Seen from the scope of implementation, these techniques can be classified in two categories, namely:

1.      Roof top rain water harvesting

2.      Rainwater harvesting techniques by building reservoirs, such as trench dams, ponds, lake, reservoir, and so on.

The difference of the two categories above is that for the first category, the scope of implementation is on the scale of individual houses in a residential or urban area while for the second category of the broader scale, usually for a farm in a river basin or sub-basin. Associated with a phenomenon that has been occurring in the some mountainous region of Bali, discussion on the idea of ​​harvesting rain just will discuss only the first category relates to the appropriate scope for residential or urban areas.

Traditionally people in the mountains of Bali using their roofs as a rain catcher which is then channeled into the tank, but there are also people who use the tarp as a rain catcher medium which is then channeled into the shelter are also made of tarpaulin. In some locations people even make a large building as rain water capture media and the inside of the building can be used as a storage crop and so on.

Figure 1. Water Spum

As the name implies, rainwater harvesting techniques to the roof of the building, in principle, be done by utilizing the roofs of buildings (houses, office buildings, or industrial) as a rainwater catchment area where the rain water that falls on the roof and then channeled through gutters to be collected and stored for further in tanks or rainwater tank. Apart formed the tank or vessel, where rainwater can also be plain water vat or in a pond / garden inside the house. Rainwater harvesting techniques that take advantage of the building's roof is commonly done in residential areas / urban.

Al Amin et al (2008) mentioned that the construction of the building rainwater harvesting can be made ​​quickly because quite simple and easy to manufacture. The main components rainwater construction consists of: the roof of the house, collecting ducts, filters to filter out leaves or other debris transported by water, and rain water tank.

Heryani (2009) in her article titled Rain Harvesting Techniques: One Alternative To Meet the Needs of Domestic Water explained that the potential amount of water that can be harvested from the roof of a building can be determined by a simple calculation, as follows:

The amount of water that can be harvested = Area X rainfall runoff X coefficient

As an illustration (as shown in Figure 2), for the province of Bali with rain catchment with an area of ​​200 m², the average annual rainfall of 2112 mm, the amount of water that can be harvested is determined as follows:

    Figure 2. Illustrations building a rainwater from the roof of the house

    With an area of 200 m² catchment rainfall, and rainfall amount of 2112 mm per year, the volume of rainwater that falls on the site:

= 20.000 dm² x 21,12 dm = 422.400 liters

Assuming only 80% of the total rainfall that can be harvested (20% is lost due to evaporation or leakage), the volume that can be harvested:

= 422.400 x 0.8 = 337.920 liters / year.

Assuming standard needs clean water for 1 person is 60 liters / person / day or a total of 21,900 liters / year, then the amount of rainwater catchment is able to meet the water needs of 15 people. The number is even able to provide a clean water supply for more than one family.

Method of catching rain water is very simple and easy to do, so this method could be an alternative to overcome the water crisis that occurred in Bali. However, the water extraction method needs to be developed to get clean water with quality standards that have been defined. The water quality of the catch must go through quality testing in order to conform to the quality standards required by the government. Moreover, this method should also be synergized with the spatial arrangement of the city to be developed into mass residential zones, trade and services, or even the government zone. Thus rainwater catchment no longer be activity per depressed individuals / families but rather a system that stands in the scale of the city. This method bias studied more in depth in order to capture the water system through the building's roof bias organized into a network system like a network of drainage channels, drains, and so forth.

The synergy between the various components of the urban spatial structure by the method of catching rain water will further maximize the production of clean water in the province of Bali. Obviously this method to the synergy city planning documents should be arranged in a legal framework for the development of methods of catching rain water can be done with very maximum.