The value of a raindrop

Rainwater is as usable to the industrialised North as to the underdeveloped South. As important to the poor, rural household as to the gardens and kitchens of the rich. Its value is universal

Published: Thursday 15 October 1998

The value of a raindrop

After battling both water scarcity and floods, the Sumida City in Tokyo has become a trailblazer in catching and using rainwater

Rain falling in the reservoir area is a must whereas rain falling in the communities is a nuisance, thinks the average person in Tokyo. Makoto Murase, director of urban affairs at Tokyo's Sumida City, is trying to change this.

Japan's capital uses 2 billion tonnes of water each year. The water comes from huge dams built far away in up-stream areas. Tokyo is short of water once every few years. And whenever that happens, it is time for another dam up-stream, leading to displacement and conflict with up-stream communities. At the same time, the 1,500 mm of rainfall it receives each year is not spared a thought. Almost 60 per cent of Tokyo's ground is covered - a city robed in asphalt and concrete. So when the rain falls, the overloaded and overflowing sewage system gives floods. This is the making of an irony of ironies: a parched city prone to floods.

Some 16 years ago, a serious flood inflicted heavy financial and health losses in Sumida City, one of the most densely populated wards in Tokyo. Floodwaters inundated many of the ward's buildings with sewage-contaminated water. For weeks people had no drinking water, as the city's drinking water tanks are installed underground.

The situation piqued Murase, who was then working in the public health centre of the local municipality, to find ways to utilise rainwater. "Rain is an incredibly important resource. It is essential to city planning and to mitigate water shortages, control flood and disasters," says Murase. "But," he laments, "society simply throws it away."

How should it be used? Build numerous mini dams -i-Murase's description of tanks that store rainwater - in cities. This not only reduces the city's water demand and reduces the pressure on water supply but also saves the environment. Large tracts of farm and forest land that large dams devour are also spared.

Moreover, rainwater is free. Its users save money. The civil servant thinks Tokyo is an ideal situation to reap the benefits of collecting rainwater as it is covered in concrete. Being the ideal for numerous cities around the world in terms of industrial development, Tokyo is now setting an example in the use of common sense in collection and utilisation of rainwater.

In the meantime, Sumida City has carried on with innovative measures to use harvest rainwater. Rainwater utilisation policies have been promoted with three aims: developing water resources in communities, restoring the regional natural watercycle, and ensuring water supply for emergencies. The ward office can boast of a rainwater utilisation system that covers half of the building's water needs and saves 1.8 million (us $) 3,500 at present rates).

A major achievement has been the installation of the rainwater harvesting facility at Ryogoku Kokugikan, a well-known Sumo wrestling arena in Tokyo. Rainfall on its 8,400-square metre roof drains into the 1,000-cubic metre storage tank. It is used in the stadium's flush toilets and air-conditioning facilities. About 70 per cent of the facilities at Kokugikan use only rainwater. Sumida City now offers subsidies up to 1 million (us $7,500} per rainwater utilisation project.

Other areas of Tokyo are following suit. A number of local governments in Tokyo, including those of Okinawa Prefecture, Takamatsu City, Toyota City, Kamakura City and Kawaguchi City have started subsidising and loaning funds for installing rainwater harvesting and utilisation systems. About 500 public facilities in Tokyo have already introduced these. The Tokyo dome, a gigantic multipurpose hall which hosts baseball games and concerts, already uses rainwater. Capturing of rainwater is also becoming popular with individual households, which are adopting full-scale rainwater utilisation system.

Along with water has come fame. And as most things Japanese, the fame and the technology has travelled to the US. Even urban planners in New York are showing interest in rainwater harvesting, says Murase. The us-based International Rainwater System Association approached Sumida City to hold a conference on rainwater harvesting. The outcome was the Tokyo International Rainwater Utilisation Conference (TIRUC) held in Sumida City in 1994.

The first conference of its kind, it featured 800 participants and was attended by thousands from across the world. The conference was also the first to focus on rainwater collection and utilisation from an urban perspective, particularly that of the "mega city". It was organised and supported by citizens and funded through the efforts and enthusiasm of people in Sumida City and its neighbouring areas.

After the 1994 conference, Murase has gained the attention of a number of citizens and municipalities. More than 85 local governments have formed a network. Citizens' groups are willing to contribute as well.

In March 1995 after the Great Hanshin earthquake, the organising committee for TIRUC presented 100 rainwater tanks of 200 litre capacity. These were used to store drinking water supplied by wagons to communities in Kobe City. The city's water supply system was totally destroyed by the earthquake.

Rainwater in government policy
In the last week of August 1998, six government ministries and agencies of Japan announced that they will jointly draw up water conservation policies. These will include restrictions on the use of groundwater and promotion of rainwater use. The policies are to be approved by the cabinet by 2000.

The administration wants to curb construction of plants in up-stream areas, prevent deforestation and urban development and discourage the use of groundwater during a water shortage.

The six government outfits involved are: the environment agency, the construction ministry, the national land agency, the health and welfare ministry, the ministry of international trade and industry, and the ministry of agriculture, forestry and fisheries.

They will coordinate policy-making to prevent floods and water shortages in urban areas, among other things. The plans will also promote afforestation and the use of rainwater recycling facilities.

Catching rainwater makes sense even in an industrialised economy. German municipalities have devised a taxation system to encourage it

Situated at the summit of the modern industrialised world, Germany does not lack water. The country is humid and rainfall is plenty. Perennial streams, rivers and lakes are numerous, and groundwater is accessed with ease. Why should it need to capture rainwater? Yet it is doing so.

In 1992 and 1993, water emergency was declared in parts of the state of Hesse. Groundwater levels in the urban areas of Frankfurt fell so low that plants started dying. Lakes and rivers fell dry. Public water supply in Germany is heavily dependent on groundwater reserves. With rivers heavily contaminated by industry and agriculture, groundwater accounts for 72 per cent of the water supply.

There is no tradition of rainwater harvesting in Germany. o But things are changing. Good quality water is difficult to find. Cost of clean water is spiralling at 11 per cent each year, rising much faster than the average cost of living. Collection and utilisation of rainwater is becoming popular.

The average German uses 144 litres of high quality drinking water every day. Only five litres out of this is for drinking and cooking, the rest being used for bathing, cleaning and flushing of toilets, among other things, where water quality requirement is not so high. Efforts are on to find economical ways to substitute 'drinking water1 with 'use water'. On the lines of "low-energy houses", there is an increasing need for "low-water houses".

There are no negative health effects of rainwater, as in the case of other 'use water'. An example of this is refined river water, which people are understandably reluctant to use for purposes of personal hygiene. A 1998 study on 102 rainwater systems for one to four years concluded that in 95 per cent of the cases the bacterial quality was better than the European standard for bath water.

Most rainwater, mainly from roofs and paved surfaces, flows into the sewer. This puts additional pressure on the sewage drainage system and sewage treatment plants, which are at the end of the sewage system. This also adds to the sewage treatment costs. Moreover, in periods of heavy rain the retention capacity of the sewerage is exceeded to unmanageable levels. When this happens, the surplus water has to be released instantly into the river. This is untreated water. It not only it contaminates the river but also leads to floods downstream. The old city of Cologne has been regulary flooded in the recent past due to this. Utilisation of rainwater reduces the amount of rainwater going into the drainage system. Costly expansions can be avoided or deferred. Using rainwater sorts out a range of problems.

Pressure on the drainage system can also be reduced by adding infiltration swales or depressions to the collection system. Unwanted water can overflow into a small pond in the garden, where it can slowly infiltrate into the ground. While the groundwater in the catchment areas is saved by reduced demand, the groundwater level is improved by infiltration.

Thilo Hermann, hydrologist at the University of Hanover, is enthusiastic about this "synergy". He found out from his research that such a combined system, if properly designed, allows more infiltration into the ground as compared to a natural situation.

So why not use this water? The cost of installing rainwater utilisation equipment for a single unit house ranges from Deutche Mark (DM) 5,000 to DM 10,000 (us $2,900 to US $5,800 at present rates). The cost is compensated by the lower water bills, and can be recovered within 10 years.

Cooperation from municipalities
The connection between economy and ecology is increasingly becoming clear, especially in the case of water. In the recent past, German municipalities have started realising the problems connected with the inflow of surface water in the sewer system.

There is an effort to streamline water management. Municipalities have developed a tax system to promote rainwater harvesting. Residents are charged separately on the basis of paved and sealed areas in their houses, such as backyards and drive-ins. A tax inspector measures the paved area roof area to calculate the amount of run-off it will generate. Tax is levied according to this. Since July 1992, there is a levy of DM 1 (us $0.58 at present rates) per cubic metre of freshwater flowing into the sewer. The funds are used to protect groundwater resources.

Residents who have set up a system to catch rainwater or have left the above-mentioned areas unpaved are exempted from the tax. This is a monetary incentive to popularise rainwater harvesting.

The tax works as a lever to motivate people to unseal paved areas and use rainwater. Using the rainwater also lowers the water bills, saving money in the bargain. Facilities to collect water for one's own use are also being encouraged, and do not need official permission. Wherever it is technically and economically feasible, provisions for infiltration of stormwaters are legally binding for new constructions.

With the pressure on house-owners growing steadily, the number of companies offering tanks, pipes, pumps and services for rainwater utilisation is increasing rapidly in anticipation of a lucrative market. Manufacturers and traders of equipment see a business opportunity in this. "The cake is growing slowly, but steadily," says Dietmar Sperfeld, spokesperson for the Association for Rainwater Utilisation, Frankfurt.

Rain, water, and an airport
Frankfurt Airport is the largest in Europe. In 1993, a new terminal was built to cater to 13,000,000 people per year. A new rainwater harvesting concept was developed for the terminal. The 26,800-square metre roof of the terminal receives 16,000 cubic metres (m3) of rainwater each year. The rainwater is collected in six 100-cubic metre tanks under the ground. It is supplied for cleaning, gardening and flushing toilets.

The plan for the terminal included the supply of 80,000 m3 of refined riverwater, which is unfit for drinking, for the air-conditioning system. The unique project saves 100,000 m3 of drinking water every year. Half the money for the project came from the state. The rest was planned to be recovered by saving the money which the airport would have had to pay in four years for the supply of water.

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