Every morning, many people press the switch on an electric kettle to prepare a warm cup of water for the day. But few realize that this familiar daily habit, if done incorrectly, may gradually introduce harmful substances into the body.

An ordinary household kettle, when misused over a long period, can quietly become a source of accumulated toxins. Below are three common water-boiling habits that many people overlook, yet which may pose potential health risks to the whole family.

---

1. Reboiling Old Water Repeatedly

Many people have the habit of leaving leftover water in the kettle overnight, adding fresh water the next morning, and boiling it again to save time and effort. However, repeatedly boiling the same water can cause certain harmful substances to accumulate.

When tap water is boiled for the first time, nitrite levels are relatively low. But with each repeated boiling, as water evaporates, nitrites remain while new nitrates are added from fresh water. Over time, nitrite concentration can increase significantly.

Once ingested, nitrites may react with amines in the stomach to form nitrosamines, which are known carcinogenic compounds. Long-term consumption of repeatedly boiled water may increase the risk of digestive system cancers, especially stomach cancer.

Key point: Fresh water should be used each time, and leftover water should not be reheated multiple times.

---

2. Keeping the Kettle Lid Tightly Closed While Boiling

Some people tightly close the kettle lid while boiling water to retain heat. However, this practice may trap volatile chemical byproducts inside the water.

During boiling, disinfected tap water can release chloroform and other disinfection byproducts. Normally, these substances evaporate with steam. When the lid is sealed tightly, these gases cannot escape and instead dissolve back into the water, increasing their concentration.

Prolonged heat retention under a closed lid may further intensify this effect. Chloroform exposure has been associated with liver damage and increased cancer risk when consumed over long periods.

Key point: When boiling water, the lid should be slightly open to allow volatile substances to escape.

---

3. Using Old or Heavily Scaled Kettles

Limescale at the bottom of kettles is often mistaken for harmless mineral residue. In reality, scale can trap heavy metals such as lead, cadmium, arsenic, nickel, or chromium, depending on water quality and kettle material.

As kettles age and are repeatedly heated, these metals may gradually leach into the water. Scrubbing only removes surface deposits, while deeply bonded compounds cannot be eliminated through simple cleaning.

Long-term intake of heavy metals may lead to accumulation in the liver, kidneys, and nervous system, increasing the risk of chronic toxicity and neurological disorders.

Key point: Kettles should be descaled regularly and replaced every few years, especially if heavy buildup is visible.

---

Safe Water-Boiling Practices to Protect Health

To reduce potential health risks, consider the following recommendations:

• Always use fresh water; avoid reheating old water.

• Leave the kettle lid open or partially open while boiling.

• Descale kettles regularly and replace them every 2–3 years.

• Use clean, regulated tap water rather than water from unknown sources.

---

Proper water-boiling habits may seem minor, but over time they can have a meaningful impact on long-term health. Small daily adjustments can help ensure that something as simple as drinking water remains safe and beneficial for the whole family.