Does Rainwater Harvesting from Roofs Solve the Water Problem?
Within the scope of Istanbul Water and Sewerage 2053 Master Plan studies, the rainwater harvesting potential of Istanbul in 2053 is estimated as 80 million m3 per year. This corresponds to approximately 3 weeks of water in Istanbul's summer months with today's usage.
Rainwater harvesting is a system that allows rainwater to be captured and stored by various methods (roof-type harvesting systems or underground storage areas) during peak rainfall so that it can be used during periods of low rainfall.
Thus, rainwater harvested by various methods can be used either directly, by simple filtration or by purification for irrigation of vineyards, gardens and agricultural irrigation and irrigation of green areas in cities, thus preventing the use of clean water (drinking water) for such uses.
In a simple rainwater collection system in the house, rainwater collected from the roof is passed through a filter that retains large particles and then comes to the rainwater tank. From the rainwater tank, it is pumped to the areas needed in the house such as washing machine or toilet reservoir.
Some of our municipalities have made some changes in their zoning regulations and the general directorates of water and sewerage administration have made some changes in their legislation on this subject.
For example, in Istanbul, in Article 40 of the Istanbul Zoning Regulation dated 20 05 2018 and numbered 30426, it is obligatory to collect the environmental drainage and roof water of the parcels over 1000 m2 in a separate cistern or the collected water must not be connected to the wastewater network.
In addition, with the amendment made to the IMM Zoning Regulation in January 2021, it has become obligatory to collect Roof and Ground Water in the cistern to be created underground in public buildings, shopping centres and commercial buildings with a construction area exceeding 5000 m2 in parcels over 1000 m2.
In this context, rainwater harvesting pilot projects have been initiated in Beşiktaş and Kadıköy municipalities in Istanbul.
Again, within the scope of Istanbul Water and Sewerage 2053 Master Plan studies, the rainwater harvesting potential of Istanbul in 2053 is projected as 80 million m3 per year. This corresponds to approximately 3 weeks of water in Istanbul's summer months with today's usage.
However, additional legislative changes, effective urban transformations and new infrastructure investments are required for the reuse of both grey water and rainwater potentials.
How widespread can the application be?
In European countries, rainwater harvesting systems have become compulsory in airports, stadiums, military areas and other places that are suitable for collecting more water, but they are also being implemented more and more in buildings.
Since the cost of the installation installed inside the building of rainwater use is higher than the cost of the installation installed and used outside, rainwater is usually collected and used outside with external drain pipes.
In our country, the average annual rainfall varies greatly according to the regions. For this reason, this application may gain priority especially in regions where rainfall efficiency is higher.
A person's grey water use corresponds to approximately 65% of the water he/she consumes daily. Rainwater harvesting can find a wider application area when considered together with the recovery of less polluted grey water (bath, shower, sink) used in homes. In this sense, this issue can find a much more widespread application area by making the second installation where grey water will be collected compulsory in addition to rainwater harvesting in new constructions and urban transformation projects.
Is it too late in terms of infrastructure?
Collecting rainwater from residential roofs does not require a large and complex infrastructure. However, it is important to determine the quality of the water before reuse. A simple filtration or pre-treatment plant may be needed to determine whether a pre-treatment is required.
In order to reduce the earthquake risk in Turkey, urban transformation projects will be implemented in many cities. In these projects, it is of great benefit to make and implement the legislative arrangements for the collection of rainwater and the reuse of slightly contaminated domestic grey water without delay.
In our country, the "Regulation on Stormwater Collection, Storage and Discharge Systems" entered into force in 2017 for the dissemination and use of this method.
This study has been an important step for progress in this field. However, in order to create a more widespread application area, a pilot region should be selected in the reconstructed buildings in the earthquake zone and an application for the combined use of rainwater harvesting and grey water should be initiated.
