**7. Underground water cistern**

Although Jeddah does not get too much rain, but it is subject to serious seasonal precipitation. In the historical houses, rainwater was harvested and collected in

*Sustainability Features of Jeddah Traditional Housing DOI: http://dx.doi.org/10.5772/intechopen.98735*

**Figure 26.** *Rooftop and underground cistern of Nasif house.*

underground massive cisterns "*saharij*" with vaulted ceilings for domestic use along the following months. This system works only on gravity without pumps, only pipes from exposed roofs to a tank below. The rate of rain may be as little as 0.5 cm in some seasons, yet it was very necessary. However, family members used to clean up the roof at times when rain is expected in communal gathering known as favor "*fazc a*". The rainwater will be directed to the drainpipes that carry it to the lower tank (**Figure 26**). This water harvesting system does not then require pipes throughout the city. These underground cisterns were also found in non-residential buildings like the masjid.

Nowadays, the only reliable source of water for Jeddah is desalination which provides 972,400 m3/day for 3.4 million residents. Desalination processes cost the Saudi authority about 1.87 US\$/m3, at a total daily cost of 1,818,388 US\$. Only 2% of desalination cost is paid by the residents at a rate of 0.04 US\$/m3, while the rest is heavily subsidized by the government [22].

A recent study proves that rainwater harvesting is still feasible, and it can significantly decrease desalination cost if applied in each house. Relying on energy, and corresponding environmental impact, can thus be limited. The study illustrates that rainwater harvesting from rooftops can help reducing the effect of urban flooding and accordingly the amount of water emitted in the sea threating the marine life. It can also reduce the possibility of raising water table which threatens the durability of buildings [23]. It is argued however that the water cisterns on the ground floor may have helped to cool the lower part of the houses [24].