Everywhere I’ve lived where it actually does get to -40, none of the pipes burst if you lose power for extended periods. First, they’re buried well below the frost line, and secondly, there’s usually an pressurized air inlet nozzle somewhere so you can open a faucet and blow all the water out if you’ll be gone for a long time.
Fun fact, -40 is the same in F and C so it’s fine to omit the units for once!
