be extracted from the well was stated as 500,000 cubic meters (500,000,000 litres per year), though due to annual variations in rainfall patterns there exists a lot of deviation with regards to how much water can be extracted without lowering the well's water level too drastically each year. Hydrogeologically, the well is in the Wadi Ibrahim (Valley of Abraham). The upper half of the well is in the sandy alluvium of the valley, lined with stone masonry except for the top metre (3 ft) which has a concrete "collar". The lower half is in the bedrock. Between the alluvium and the bedrock is a section of permeable weathered rock, lined with stone, and it is this section that provides the main water entry into the well. Water in the well comes from absorbed rainfall in the Wadi Ibrahim, as well as run-off from the local hills. Since the area has become more and more settled, water from absorbed rainfall on the Wadi Ibrahim has decreased. The Saudi Geological Survey has a "Zamzam Studies and Research Centre" which analyses the technical properties of the well in detail. Water levels were monitored by hydrograph, which in more recent times has changed to a digital monitoring system that tracks the water level, electric conductivity, pH, Eh, and temperature. All of this information is made continuously available via the Internet. Other wells throughout the valley have also been established, some with digital recorders, to monitor the response of the local aquifer system. Zamzam water is colourless and odorless, but has a distinctive taste, with a pH of 7.9–8, and so is slightly alkaline. Safety of Zamzam water The Zamzam Well is tested on a daily basis, in a process involving the taking of three samples from the well, and that these samples are examined in the King Abdullah Zamzam Water Distribution Center in Mecca, which is equipped with advanced facilities. The Zamzam well was recently renovated in 2018 by the Saudi authorities. The project involved sterilisation of the areas around the Zamzam well by removing the debris of concrete and steel used in the old cellar of the Grand Mosque. During Ramadan, 100 samples are tested every day to ensure that the water is in good quality. Historical controversy Cholera epidemics and the Hajj had become an issue of debate since a 1866 CE International Sanitary Conference in Istanbul. The conference however identified British