Boil Water

You think boiling water is easy, right? You just heat the water until it starts bubbling. But there's a little bit more to it than that, especially if you want to be a precise and most excellent cook.

Stovetop

 * 1) Know what kind of boil you're going for. Poaching, simmering, and boiling are slightly different techniques. Poaching is very gentle, reserved for delicate foods like eggs, fish, and fruit. Simmering is a little hotter, with a few small bubbles rising to the surface, and is often used for items that need a long time to cook. Boiling is when the water gets as hot as it's going to get and begins to evaporate into steam. (The exact temperature varies by altitude, as discussed in the next step.) Get the water to whichever state the recipe calls for and keep it there. Don't place a lid on the pot if you're poaching or simmering because the heat may increase to a boil. Remove from heat if necessary if the water starts to get too hot.
 * 2) Consider your elevation. At higher altitudes, water boils at a lower temperature, so you'll need to cook the food longer.
 * 3) *If you're cooking anything that comes with instructions, look for a note about altitude that will tell you what adjustments need to be made.
 * 4) *At especially high altitudes (like on mountains), you might boil something for hours and hours and it'll never cook. You'll need to use a pressure cooker.
 * 5) *Since liquids evaporate faster at higher altitudes you should also add a little extra water to compensate.
 * 6) Add salt only for seasoning or making eggs easy to peel. There's a myth that adding salt will make the water boil faster. Adding salt raises the boiling point, which means the water will need to be hotter to begin boiling, therefore actually taking longer to boil. Don't avoid adding salt to taste, however, because the amount of salt it'd take to make any significant change would probably be enough to ruin whatever you're cooking. In one home experiment, adding 2 tablespoons of table salt to 1 liter of water caused it to take an additional 33 seconds to boil, and it increased the boiling temperature by only 4°F (2°C). For some added perspective, you need the salinity of ocean water (an ounce of salt per quart of water) in order to raise the boiling temperature by just one Fahrenheit degree!
 * 7) Use a large enough pot for the water you are heating and don't fill it all the way. The extra space will give the water somewhere to bubble and splash. You will also need enough extra space for anything (such as pasta) you will add to the water later.
 * 8) Place the pot on the stove and turn the heat under it to high. Covering the pot with a lid will help the water to boil a little bit faster.
 * 9) Turn down the heat once the water starts boiling. High heat is useful when you want to get the water to reach boiling temperature quickly, but once it's there, turning up the heat won't make a difference in temperature. All it'll do is cause the water to boil away faster. So once the water is bubbling, turn down the heat to the lowest temperature that will keep it at the boil you need. This will help you retain more water and will also be neater and safer, since rapidly boiling water is more likely to splash out of the pot.

Microwave
Boiling water in the microwave is pretty straightforward, but there is the risk of superheating, when the water heats up past the boiling point without bubbling and then erupts suddenly, possibly causing burns. While this is unlikely there are some precautions you can take.
 * 1) Put the water in a microwave-safe cup or bowl. 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.
 * 2) Place a non-metallic object such as a wooden spoon, chopstick, or popsicle stick in the water. This also helps the water bubble.
 * 3) Put the water in the microwave. Heat in short intervals, stirring regularly, until the water is steaming. (Even if these steps are followed, bubbling won't be obvious.)
 * 4) Stir the liquid thoroughly to add a little air to the mix, before heating.

Tips

 * If you are boiling something other than water, such as sauce, turn it down as it reaches boiling to avoid scorching the bottom to the pot.
 * If a recipe calls for something to be at a "full, rolling boil" it means that the water should not stop boiling when you stir.
 * Hot water boils faster than cold water.

Warnings

 * Boiling water and the steam coming off of it are hot enough to burn you. Use a pot holder if you need to, and handle with care.
 * Steam will scald more than boiling water due to the extra heat energy it contains
 * Watch out if heating distilled water in a microwave as it can explode when picked up. (flash boil)

Related Tips and Steps

 * How to Cook
 * How to Boil Eggs
 * How to Use a Pressure Cooker