Falaj Daris is one of the oldest active aflāj located in Oman and the largest in the Dakhiliyah governorate. It is a 7,999-meter long Dāwūdī-type falaj. Ninety-five percent of water drawn from falaj Daris is used for agricultural irrigation and the remaining five percent is used for domestic purposes. In this paper, we analyzed several datasets including falaj Daris discharge, borehole water levels in wadi al-Abyadh, whose aquifer falaj Daris taps, and GRACE satellite data to determine the historical trend of falaj Daris discharge during 1982-2020. A set of standard statistical methods and data visualization techniques were applied including the Mann-Kendall trend test. Preliminary evidence shows a decline of 226,000 L/day in falaj Daris discharge between 1982-2020. This finding is supported by the overall trends in borehole water levels in wadi al-Abyadh. All these trends were confirmed using GRACE satellite data which shows a decrease in water volume of 6 (WET cm) in the larger basin between 2002-2021.