Undoubtedly, water is the most precious and indispensable natural resource. However, in recent decades, human societies consume fresh water recklessly and wastefully, by considering that water reserves are inexhaustible. For this reason, in the last decades, scientists focus on studying the sustainable management of water resources, part of which are the methods of collecting and use rainwater.
This paper presents a study of an environmental management plan for the installation of a rainwater harvesting system which will serve the demands for toilets and irrigation of an educational institute. Particularly, the case of International Hellenic University, Department of Forestry and Natural Environment in Drama, Greece has been studied because the drainage surface of rainwater of the building is large enough for the collection of considerable quantity of water, and the consumption of drinking water is small in contrast to the non-potable water, which is mainly used for different purposes in various departments of the Institute, such as toilets, laboratories and gardens. According to the construction design, the building is divided into six sub-sections, and the total roof surface is 3,882.77 m². Additional, a greenhouse has been built, with total area of 90 m². Also there is a large green area of approximately 78,000 m², mostly unexploited, in which there are some ornamental trees and shrubs, roads and parking spaces.
Firstly, field observation and recording of the existing rainwater network and of the existing damages and construction errors became, while at the same time restoration is proposed in order not to reduce the qualitative and quantitative performance of the rainwater collection system.
The drainage volume of water that can be collected by each sub-section and the total area of the roof of the building, and the total required amount of water for the needs of the institute analyzed and compared for each month. Comparing the results is noted that the harvested rainwater is able to cover the 100% of needs for water, for toilet flushing and cleaning of the institution, or the 40.55% of total consumption of water from the institution for non-potable use (toilet flushing, cleaning and irrigation).
The sizing of the tank became by applying one of the most common methods which relates the dry season (Ndd) with the annual rainwater yield (ARY), and the annual demand of rainwater (ARD).
In the case study, the calculation of volume of the tank is made according to the meteorological data in the region, for the period 2000-2010, of which the average annual rainfall P is 713.03mm, and the mean maximum dry season is 19.6 days.
Consequently the total volume of tanks is calculated at 133.80 m³, which obviously is quite big and therefore more than one tank will be installed. The installation of seven underground, cylindrical tanks of reinforced concrete is the ideal solution both in terms of construction, operational and economic. The RWH system will also include the installation of calming devices, pipes, grills, screens, first flash diverters, pumps, reverse flow prevention device etc. It is therefore very important to pay special attention to good quality of materials and proper maintenance of the roof, pipelines and tanks, to ensure water quality safe for consumer health.
Finally, the institution will not have a direct economic benefit, as it does not being charged by consumption of public water network. Nevertheless, it should not underestimate the environmental benefits arising from the application of the RWH system, which cannot be estimated at financial units.