Tried to install a new faucet today, connecting to some old pipes, to old eccentrics, to be exact. These had some ancient locks/valves, which probably broke when I was attaching new fittings, so the water started exploding into my face.
After turning off the main valve, the pressure of the leakage dropped but the water kept coming out of the broken valves, possibly due to the pressure from the water heater. Installed some blinds and case closed for now. Will look to replace the eccentrics tomorrow.