Rainwater harvesting and storage do not constitute a new technology. Small dams and runoff control means for agricultural purposes can be traced back to early history. An example of this are the rice terraces in the Philippines. In use for thousands of years, they still prove to be an efficient technique today. The use of earth dams to control runoff was also known in ancient Egypt.

Archaeologists found a sophisticated rainwater collection and storage system on the island of Crete while working on the reconstruction of the Palace of Knossos (1700 B.C.). However, with the development of building construction based on new materials such as lime and burnt clay bricks, new construction techniques like arches and domes developed. The ancient Romans became masters in rainwater harvesting and the construction of reservoirs. It was this new technique of building closed cisterns, and at the same time the urbanization within the Roman Empire around the Mediterranean, which resulted in the development of a rainwater catchment culture at all those places where water resources were limited. This is why old rainwater cisterns are to be found on the islands of Capri and Malta and at places of historical interest in Spain and Turkey, in the Lebanon and on the island of Sicily.

It appears that the rainwater harvesting technique used in the Roman houses was based on the experience gained in Knossos.

"Through a small anteroom (vestibulum) a closed internal court is reached (atrium) which has a pool in the centre into which the rainwater from the roof flows. The pool is lined inside with ceramics and has sloping sides. The atrium is closed behind by the sitting room (tabunium) which leads into a larger internal court (perstilium) where a second pool collects water from the roofs of the rooms surrounding the court''.

Many of the ancient systems, including the Roman rainwater catchment techniques for housing, served a double purpose. The evaporation of the water in the pools improved the microclimate through its air-conditioning effect, and the water was used for domestic purposes. As a result of urbanization, increased density of plot coverage and growing population, the consumption of water also increased. This led to the development of covered cisterns. These were built in the ground underneath the courts. This had two major advantages: firstly, the amount of water which could be stored was increased considerably and evaporation losses were reduced. Secondly, the cisterns served as a protection against pollution of the water. The more sophisticated houses still had the shallow pool in the atrium. All the rainwater from the roofs flowed into the pools and an overflow drained into the cisterns. At this time rainwater catchment techniques were decentralized, and this may be the reason why they lost momentum with the increasing consumption and the development of a centralized supply from springs channelled into the urban areas. However, few examples of centralized rainwater catchment and storage in cisterns are known.

Probably the world's largest cistern is the Yerebatan Sarayi. On the European side of Istanbul in Turkey, it was constructed under Caesar Justinian (A.D. 527-565) and measures 140 by 70 metres. It can store 80,000 m³ water. The underground structure is based on intersecting vaults. Nowadays it has turned into a tourist attraction which can be visited by boat, drifting through a forest of columns. Another cistern in Istanbul is called Binbirdik and has a capacity of 50,000 m³. Sources are unclear as to which of the cisterns is the older. It could be the Binbirdik if constructed under Caesar Constantine (A.D. 329 - 337) as one source suggests. Both cisterns served as centralized storage. The water was collected from roofs and paved streets and a sophisticated system of filters assured clean water. However the municipal underground cisterns in Istanbul are probably the only examples of urban centralized rainwater harvesting of their kind. There are probably two major reasons why this technique was no longer used. Firstly, the construction of underground cisterns is considerably more expensive than the construction of dams. Secondly, there is a danger of accidental pollution through human excrete in dense urban areas and therefore a risk of epidemics.

Although rainwater harvesting and storage in closed cisterns were never used again to the same extent as in ancient Rome, they were occasionally employed where circumstances demanded an appropriate technology. This happened in semi-desert areas where people wanted to build homes without springs or wells in the vicinity. The technique was often used when Christian monks built their monasteries. Many of these examples still exist in the former Spanish Empire and monasteries in Mexico, for instance, provide evidence of the high standard of design and construction.

The technique disappeared with increasing urbanization. It can be assumed that the technical means available during the industrial age, the need for supplies of large amounts of water for industry, the high standard of water hygiene achieved through central treatment and safe supply via pipes are all reasons for the reduced use of rainwater harvesting. But modern water technology not only has advantages. Its disadvantages are as follow:

-The centralization of supply involves the risk of total cut-off in cases of natural disaster (earthquakes etc.), destruction through acts of war (bombing etc.), and source pollution (environmental pollution through chemicals). This is the vulnerability of a modern centralized water supply.

- The consumption of water is not only based on need, but very much influenced by the convenience of access. It can be observed everywhere that water wastage is the rule rather than the exception. This is based on an economy which has made one source of life a commodity of consumption and represents the contradiction between the need for careful management of world resources and an economy based on permanent expansion. However' in general there can be no doubt that there is no alternative to a centralized water supply in urban areas nowadays.

Rainwater harvesting is gaining importance again, this time in rural areas and especially so in many developing countries. The present situation in developing countries demands the utilization and development of all possible sources to ensure the supply of water.

Much has been published about rainwater reservoirs for rural housing. Less emphasis is given to the construction of large reservoirs as stand-by facilities. Likewise not much is known about the possibility of using rainwater as raw. water and by doing so of reducing the consumption from centralized supply. The following section will show that the use of rainwater combined with the saving of water and reuse of waste water can be an economic solution when considering the rising cost of pipeborne water.