Cold temperatures cause the pressure in your fuel canister to drop. But your stove needs that pressure to run strong. To help keep a stove running at full output when its canister pressure is low (i.e., in cold temps), some stoves like MSR’s Reactor and WindBurner stove systems and PocketRocket Deluxe stove feature a pressure regulator. The regulator is a complicated engineering component, but its purpose is to keep your stove running strong in conditions that shut down unregulated stoves.
However, in freezing temps, the pressure in the canister is likely to drop below what even the pressure regulator can maintain. This is when placing your canister in a bowl of water can help. So long as the water isn’t turning to ice, the temp of the water will keep the canister’s pressure up enough that the pressure regulator can maintain it–and keep your stove cranking.
So yes, the canister-in-a-bowl-of-water trick is a solid one for winter adventurers. Keeping your canisters warm in your jacket or sleeping bag prior to use is another pro tip that goes a long way toward that hot meal.
We hope this tidbit helps. Happy adventuring!