Urban floods are difficult to detect accurately in satellite imagery because non-water surfaces often resemble floodwater, causing false alarms. This study introduces an enhanced normalized difference water index (ENDWI), derived from the normalized difference water index (NDWI), combined with a second hybrid index to reduce these false alarms using freely available Sentinel-2 imagery. False alarms were reduced from 38 % to under 3 %, offering a more reliable, low-cost approach to urban flood mapping.