Why Boiler Water from Coffee Machines Is Unsafe to Drink

If you’ve ever used the hot water spout on your espresso machine to make tea, rinse cups, or even take a sip—because it’s convenient—you might want to reconsider. That water comes from the machine’s internal boiler, which is constantly kept hot and often reheats the same water multiple times a day. What seems like a time-saver could be quietly affecting your health.

Yes, repeatedly boiled water from a coffee machine boiler may contain elevated levels of harmful nitrates and even carcinogenic nitriles. Studies show that water repeatedly heated in this way can pose real risks if consumed regularly.

What Happens When Water Is Repeatedly Boiled in a Coffee Machine?

Most home and commercial espresso machines are equipped with a built-in boiler that maintains water at a set temperature using an internal thermostat. When the temperature drops, the machine automatically reheats the water. This means the same water can be boiled and reheated many times over—sometimes dozens of times a day—even if you’re not actively pulling shots or steaming milk.

While this feature ensures you always have hot water ready, it also means you're potentially consuming water that has been thermally cycled over and over. This repeated boiling is the root of the health concern.

The Health Risks of Drinking Reboiled Boiler Water

Laboratory studies have demonstrated that repeatedly boiling water can cause dissolved nitrates—naturally present in tap water—to convert into nitrites . These nitrites then interact with hemoglobin in the blood, transforming it into methemoglobin , which is far less effective at transporting oxygen.

This can lead to symptoms such as:

• Shortness of breath
• Rapid breathing
• Chest tightness
• Lips and nails turning bluish-purple
• Chronic tiredness or drowsiness

In more severe cases, nitrites ingested into the stomach can be further converted by gastric acid into nitrosamines —compounds that are known to be carcinogenic.

Why Your Coffee Machine Boiler Is Especially Risky

Unlike a kettle, which is typically emptied after each use, the boiler in a coffee machine is not designed to be drained regularly. Its job is to maintain heat constantly, so unless manually flushed, the same water remains inside for long periods and is repeatedly brought to temperature.

Even if you’re not actively using the hot water function, the machine’s thermostat ensures the boiler cycles on and off to maintain temperature—resulting in many more heating cycles than you might assume. That means the water is not just hot, but old, possibly stale, and chemically altered over time.

How Many Times Is the Water Actually Reboiled?

Although exact numbers vary depending on usage patterns, a typical home espresso machine can reheat its boiler water dozens of times in a single day—even if you never touch the hot water spout. Each time the machine cycles on to maintain temperature, the water is technically being reheated. Over weeks and months, this leads to significant cumulative reboiling.

Frequently Asked Questions

Is it safe to use the hot water from my coffee machine’s boiler for tea or other drinks?

No, it is not considered safe. The water in the boiler is often repeatedly boiled, which can increase levels of nitrates and nitrites. These substances can reduce oxygen transport in the blood and, in some cases, may form carcinogenic nitrosamines. For these reasons, it’s better to avoid drinking or cooking with water from the machine’s boiler.

Can reboiled water cause health issues?

Yes. Repeatedly boiled water may see increased nitrate conversion to nitrites, which bind to hemoglobin and impair oxygen delivery. Symptoms can include breathing difficulty, fatigue, and bluish discoloration of lips or nails. In more serious instances, nitrites can form nitrosamines, which are linked to cancer risk.

Why does my coffee machine keep reheating the water?

Coffee machines use a thermostat to keep boiler water at a constant brewing or steaming temperature. When the water cools below the set point, the machine automatically reheats it. This cycle can happen many times per day, even without active use, leading to the same water being boiled repeatedly.

Should I avoid using the hot water function on my espresso machine altogether?

It’s best to avoid using the boiler water for consumption—such as drinking, making tea, or preparing food or drinks—if you value minimizing health risks. The water has likely been boiled and reheated multiple times, increasing potential chemical changes that may affect safety.

How can I reduce risks if I still want to use the hot water?

If you must use the hot water spout, try to flush the system regularly by running fresh water through it, and avoid letting the same water sit in the boiler for extended periods. However, for drinking purposes, using freshly drawn water from a reliable source is the safest choice.

Recommended FrontStreet Beans for Home Brewing

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