How to Boil Water

Boiling Water for Cooking

Choose a pot with a lid. A lid will trap heat inside the pot, making the water boil faster. A large pot will take longer to boil, but the shape does not make a noticeable difference.

Add cold tap water. Hot tap water can pick up lead from your water pipes, and is not recommended for drinking or cooking. Start with cold tap water instead. Don't fill it all the way — a full pot can splash you as it boils, and you'll need space to add the food if you're cooking. Don't believe the myth: cold water does not boil faster than hot water. It's the safe option, but it will take a bit longer.

Add salt for flavor (optional). Salt has almost no effect on the boiling temperature, even if you add enough to make it seawater! Add it only to flavor the food — especially pasta, which will absorb the salt along with the water. You might notice a bunch of bubbles rise up as soon as you put the salt in. It's a fun effect, but it doesn't change the temperature. Add salt when boiling eggs. If the shell cracks, the salt will help the egg white solidify, plugging the hole.

Place the pot over high heat. Place the pot on the stove and turn the burner underneath it to high. Cover the pot with a lid to help the water boil a little faster.

Learn the stages of boiling. Most recipes will either call for a simmer or a rolling boil. Learn how to recognize these stages, plus a couple less common options that will help you find the perfect temperature: Quiver: Tiny bubbles appear at the base of the pot, but do not rise. The surface quivers slightly. This happens at about 140–170ºF (60–75ºC), a temperature good for poaching eggs, fruit, or fish. Sub-simmer: A couple little streams of bubbles are rising, but most of the water is still. The water is around 170–195ºF (75–90ºC), and can be used for stew or braising meat. Simmer: Small to medium bubbles break the surface often, all across the pot. At 195–212ºF (90–100ºC), this is a good time to steaming veggies or melting chocolate, depending how healthy you're feeling. Full, rolling boil: Steam and constant movement that doesn't stop when you stir the water. This is the hottest your water is going to get: 212ºF (100ºC). Cook pasta at this temperature.

Add the food. If you are boiling something in the water, add it now. The cold food will lower the water temperature, and might reduce it to an earlier stage. That's fine; just leave the heat on high or medium until the water returns to the correct level. Unless a recipe specifically tells you to, don't add the food before the water is hot. That makes it hard to estimate the cooking time, and can have unexpected effects. For example, meat ends up tougher and less flavorful if exposed to cold water at any time during cooking.

Turn down the heat. High heat is useful when you want to get the water to reach boiling temperature quickly. Once you've got where you want, reduce the heat to medium (for boiling) or medium-low (for simmering). Once the water is at a rolling boil, more heat will only make it boil away faster. Check on the pot occasionally for the first few minutes, to make sure the water is stable at the stage you want it. When you're making soup or another long-simmering dish, leave the lid slightly ajar. Closing the lid completely will raise the temperature too high for these recipes.

Purifying Drinking Water

Boil water to kill bacteria and other pathogens. Just about every harmful microorganism found in water will die when the water is heated. Boiling will not remove most chemical contamination. If the water is cloudy, filter the water first to remove dirt.

Bring the water to a rolling boil. It's the heat that kills microorganisms, not the boiling action itself. However, without a thermometer, a rolling boil is the only accurate way to tell how hot the water is. Wait until the water is steaming and churning for at least one to three minutes. By this point, all the dangerous organisms should be dead.

Keep boiling for 1–3 minutes. To be extra cautious, leave the water at a rolling boil for 1 minute. (Count to 60 slowly.) If you are higher than 6,500 ft (2,000 m) above sea level, let it boil for 3 minutes instead. (Count to 180 slowly.) Water boils at a lower temperature at high elevations. This slightly cooler water takes longer to kill organisms.

Let cool and store in closed containers. Even after cooling, the boiled water will be safe to drink. Keep it in clean, closed containers. The water will taste "flat" compared to normal water, because some of the air inside it escaped. To improve the taste, pour the water back and forth between two clean containers. The water will trap more air as it falls.

Carry a portable boiling device when traveling. If you will have access to electricity, bring along an electric heating coil. If not, carry a camping stove or kettle, plus a fuel source or batteries.

Leave plastic containers in the sun as a last resort. If you have no way to boil water, put the water in a clear, plastic container. Leave it for at least six hours in direct sunlight. This will kill some dangerous bacteria, but it is not as safe as boiling.

Boiling Water in the Microwave

Put the water in a microwave-safe cup or bowl. If you can't find a dish labeled "microwave safe," choose glass or ceramic cookware that does not have any metallic paint. To test whether it is microwave safe, place it in the microwave, empty, next to a cup of water. Microwave for one minute. If the dish is hot after the minute is up, it is not microwave safe.{ For increased safety, use a container that has a scratch or chip (in scientific terms, a nucleation site) on the interior surface. This will help the water bubble, reducing the risk of an (already unlikely) "superheated" explosion.

Add a microwave-safe object to the water. This also helps the water bubble. Try a wooden spoon, chopstick, or popsicle stick. If you don't mind flavoring the water, even a spoonful of salt or sugar should be enough. Avoid using a plastic object, which may be too smooth to allow bubbles to form on it.

Put the water in the microwave. In most microwaves, the edge of the rotating carousel will heat up faster than the center.

Heat in short intervals, stirring regularly. For maximum safety, look up recommended water heating times in your microwave's manual. If you don't have the manual, try heating in 1-minute intervals. After each interval, cautiously stir the water, then remove it from the microwave to test its temperature. The water is ready when it's steaming and too hot to touch. If the water is still cool after the first couple minutes, increase the length of each session to 1.5 or 2 minutes. The total amount of time depends on your microwave's power and the amount of water you're boiling. Don't expect a "rolling boil" in a microwave. The water will still reach boiling temperatures, but it will be less obvious.

Boiling Water at High Altitudes

Understand the effect. Moving up from sea level, the air gets thinner and thinner. With fewer air molecules to push the water down, each water molecule has an easier time breaking away from the others and entering the air. In other words, it takes less heat to get the water boiling. The water will boil sooner, but the low temperature will make it harder to cook food. You don't need to worry about this effect unless you're at 2,000 ft (610m) or higher.

Start with more water. Since liquids evaporate faster at higher altitudes you should also add a little extra water to compensate. If you're planning to cook food in the water, you should add even more water. The food will require a longer cooking time, so more water than you're used to will boil away.

Boil food for longer times. To make up for the lower temperature, you can cook the food for a longer amount of time. Here's a simple rule for how much time to add: If the recipe would take less than 20 minutes to boil at sea level, add 1 minute of cooking time for each 1,000 ft (305m) above sea level. If the recipe would take more than 20 minutes to boil at sea level, add 2 minutes for each 1,000 ft (305m) above sea level.

Consider using a pressure cooker. At especially high altitudes, cooking in boiling water can take an unreasonably long time. Boil water a pressure cooker instead. This traps the water under an airtight lid, and raises the pressure so the water can reach higher temperatures. In a pressure cooker, you can follow the recipe as though you were cooking at sea level.