Bhandup Complex water treatment plant located in Mumbai, India, supplies water to most of Mumbai. The plant receives raw water from Vehar Lake. Alum has been used as a coagulant in the treatment process for the past 27 years. The backwashed water from the plant is released into Vehar Lake, which carries a significant amount of suspended matter. Therefore, a layer of sludge was deposited on the meeting point of backwashed water and Vehar Lake. The status of aluminum (Al) concentration in sludge deposits, banks, water, and sediment samples of Vehar Lake and its comparison with Al concentration of soil in the area surrounding the plant is presented in this paper. The comparison showed that the surrounding soil samples had the least Al concentration (16,394–26; 081 mg=kg), whereas the highest values of 53,882–73; 382 mg=kg and 62,096–76; 496 mg=kg were reported in upper and lower layers of sludge, respectively. This paper also discusses the detrimental effect of Al when it is available in toxic form at acidic ph.