A burst or failed galvanized pipe is one of the calls we answer most around here. Plenty of older Decoto-area homes still run their original galvanized supply line, and that metal corrodes from the inside over the decades until the wall thins and a section finally splits, often at a threaded joint hidden inside a wall. When galvanized lets go, it does not drip politely, it sprays, and the damage adds up quickly. By the time you see a stain on the ceiling or hear the hiss behind drywall, water has usually been moving for a while, so we treat these as drop-everything calls.
The second emergency we see constantly is a sewage backup. Several Decoto homes are still on their original sewer laterals, older galvanized or cast-iron lines that are due for inspection, and an aging clay or cast lateral that tree roots have finally choked off will push raw sewage up through a floor drain or tub. That is both a health hazard and a true emergency, not a wait-until-Monday problem. We come out, clear the blockage, and put a camera down the line so you can see exactly what we are dealing with instead of guessing.
The third is a sudden loss of hot water. Union City is served by the Alameda County Water District and shares the same moderately hard water Newark has, so heaters here scale up faster than the label promises and can fail earlier than you would expect. A tank that ran fine yesterday can be cold, or leaking from the body, today. Once a tank is leaking from the shell itself, there is no patch for it, and the only safe move is replacement before the seam opens wider and empties forty or more gallons onto the floor.