Baseline Chemical, Physical, and Microbial Properties of Graywater in Riyadh, Saudi Arabia

Graywater (GW), which includes all forms of domestic waste water except toilet waste, is an essential component of sustainable water management, especially in arid regions. However, direct reuse of raw GW may pose an environmental threat. Therefore, this work investigates the microbial, physical, and chemical characteristics of GW from different sources in Riyadh, Saudi Arabia. Samples were collected from four different sites where GW is applied and used: a house kitchen, a mosque, a hotel, and a residence in hospital. Samples were collected on a monthly basis for one year, taking into consideration the season. Microbial analysis included total colony counts, total fungal count, and counts of Staphylococcus, coliform group, Pseudomonas, Salmonella, Shigella, Streptococcus, and thermophilic bacteria. The chemical and physical variables were measured, including pH, EC, turbidity, COD, total solids, organic matter, cations and anions, TSS, TDS, and heavy metals. The results showed that the characteristics of the GW from different sources in Riyadh varied considerably between locations and seasons. Kitchen GW was highly contaminated, while ablution GW from the mosque showed the least contamination. The presence of high microbial loads suggests that the untreated GW generated in Riyadh is unsuitable for direct reuse. Therefore, appropriate treatment strategies are required before GW can be utilized in order to minimize potential risks to human health and the environment.