Should You Add Cold or Hot Water When Cooking?

When you boil pasta, do you use hot or cold water from the beginning? Hot water seems like a better decision, because it saves time for it to boil comparing with cold water. However, hot tap water faces some criticism about carrying more contaminants than cold tap water. Furthermore, the flavour and texture of food could be different using different temperature of water. Let’s explore all these possibilities!

Time-efficiency

No questions on this one, hot water boils faster than cold water in the same conditions. Even though the altitude and air pressure affect the boiling temperature of water, in the same environment, hot water still wins in boiling time-efficiency.

Other than temperature, there are other factors affecting boiling time. Less water, a closed lid, and a higher heating level means less boiling time.

Safety

In China, because the tap water is not drinkable and hot water costs more energy, we always boil cold tap water in a large kettle. After boiling, we would store the majority of water in thermos flasks and cool some down to room temperature before drinking or cooking. In the first year when I came to Canada, I knew that the tap water here is drinkable (except in some remote indigenous communities), so I simply put the tap on and got lukewarm water (out of preference) in my water bottle for drinking. Then a friend who also came from China told me not to drink hot or warm water out from the tap, and only cold water is potable. I was quite surprised, because nobody else told me that, and obviously there was no sign on the wall says so. I chose to follow her advice and started to drink only cold tap water, although I was not sure about the reasons behind it.

When it comes to cooking, I used to always boil hot tap water to make it faster. One day I was thinking, why it’s advised not to drink the hot/warm tap water? And if it’s not good for drinking, are they good for cooking? After some Googling, I found quite a few online articles (1,2,3,4) trying to say the same thing: do NOT use hot tap water for drinking or cooking! Hot water is better at dissolving than cold water, which makes it easier for lead and other contaminants to leach into the hot water. Those contaminants come from older water pipes and hot water tanks. Although the process of boiling water kills bacteria and other pathogens, it won’t kill the harmful chemicals in the water. We all know that lead is bad for you and can cause harmful effects in the long run. The amount of harmful chemicals in hot tap water might be very slight and not cause any problems in the short term, but it’s better to be safe than sorry. I’m not an expert on modern water treatment systems, and I welcome debates if you happen to know more. For me, I’ll choose to use cold tap water for drinking and cooking.

Flavour, texture, and cooking process of food

Some people noticed that hot tap water gives a slight off flavour to the food comparing with cold tap water. It could be because of the slight amount of metals hot tap water has dissolved.

There is also an observation that using hot water to start a stock with meat and bones makes the broth foamy, and cold water makes it clearer. It’s because the water with high initial temperature draws the insoluble proteins out from the meat and bones.

Cold water doesn’t always win. Sometimes we want to cook with hot water. For example, blanching vegetables requires boiling water to start and only cooks the outside of the vegetable for a short time (this is usually used for vegetables that can be eaten while raw). As another example, when you are in the middle of cooking food in a pot and you need to add some water, hot water is a better option. If you add cold water instead, the temperature of the food would drop and it would take longer to cook the food and vaporize the water. Sometimes, that also means a different texture result for the food.

The Bottomline

Always use cold tap water for drinking and cooking to be safer. If you need hot water for cooking, boil cold tap water before combining it with food. To make it more time-efficient when boiling water, you can use less water, a closed lid and a higher heating level, or choose to invest in a thermo water container or hot water boiler and dispenser.

Let me know your thoughts in the comments below!