The water supply is available in four ways:
• Connection to the urban network
• Rainwater harvesting.
• Surface water.
Connection to the urban network
It is the usual way in the urban environment . It is comfortable and offers a security of supply , both for its continuity and its quality . Often this water must be brought from relatively remote areas with the consequent pumping cost beside leakage in urban networks can lose around 30 % of total volume. In return for this service the user must pay a fixed set of concepts and other variables according to consumption . On bill not only supply but also treatment of wastewater we produce must be paid for.
Depending on the characteristics of the project is easy to harvest rainwater from rooftops , terraces or other impervious surfaces.
In Spain the average annual rainfall is 636 l/m2 so per 100 m2 floor space could obtain an annual volume of 63,600 liters . But there is much geographical irregularity in rainfall in Spain leading to large differences between the north and th rest of the country .
Average annual rainfall in Spain.
Beside to these geographic irregularities, especially in south and middle ther is a high variability of rainfall during the year , with very intermittent rain from autumn to spring and dry summer. To this is added the cycles of rainy and dry years. All this irregularity may require a large volume of storage.
Not only depend on rainfall but also the use to which will be give to that water. If we use this water for irrigation will have a time when rain fills the tank but the plants do not need watering, so the tank will be filled and overhelmed. In summer, when the plants need more watering, the tank is only emptying, and unless it is a very large volume , probably will not be enough.
In areas where it rains more regularly cycles of filling and emptying alternate, resulting in the same size of deposit will be much more effective.
These are some of the factors that have to be input in the study of the optimum storage capacity .
The main benefit of this is that water is «free and clean».
Widely used especially in rural environments and usually for irrigation although they are also used as drinking water. Are more fragile against contamination and is more difficult to detect. The price of water is lower, but there isn’t always this possibility.
The existence of illegal wells causes many problems of exhaustion and lack of quality causing major environmental problems.
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Predominantly used for irrigation. They are very sensitive to hydrological cycles and requires infrastructures that can become quite complex and expensive . From all possible sources of supply is the least usual.