No special gadgets are required.
A lot of bubbles escape the first time you crack open a bottle, meaning you’ll get maximum fizz if you just drink that La Croix right away. Unopened bottles are pressurized to help maintain the CO2 in water. Break the seal and the gas is released. But what if you’ve invested in a big ole bottle of Polar? We’re talking the 2 Liter kind. Downing that will mean a lot of trips to the you know where.
You can’t add that pressure back, so ignore specialized gadgets that claim to do so. There’s one trick that really works though, and it’s a throw back to 5th grade science class. We’re talking about solvents (liquids that can dissolve other substances) and solutes (substances that dissolve). In this case, the water is the solvent and the CO2 is the solute. Ever wonder why seltzer doesn't look bubbly until you open it? That's because pressure causes the CO2 to dissolve in it. When it escapes, it makes bubbles. More dissolved CO2 means more bubbles. Cold temperatures also cause the gas to dissolve. So keeping your opened seltzer as cold as possible is the key to keeping it bubbly. Pretty simple actually.
Store your half finished Polar or Soda Stream canister in the coldest part of the fridge--that’s the back. Or use your leftovers to whip up one of these tasty recipes tasty recipe (yes, you can cook with seltzer!). Hint: it makes for the lightest pancakes in the entire world, and delicious ice-cold gazpacho soup.