**Can water stay liquid below zero degrees Celsius?**

Water is a unique substance that behaves differently compared to most other substances. Normally, when the temperature of a substance drops below its freezing point, it solidifies into a solid state. However, water can stay in its liquid state even below zero degrees Celsius under certain conditions. This phenomenon is known as supercooling.

**Supercooling: An Extraordinary Property of Water**

Supercooling occurs when the temperature of a substance is below its freezing point, but it remains in a liquid state. Water can supercool due to its specific properties, such as high surface tension and purity. Here's how it happens:

1. **High Purity:**
- Pure water without any impurities or nucleation sites can supercool easily.
- Impurities in water, such as dirt or minerals, can act as nucleation sites, promoting ice crystal formation.

2. **High Surface Tension:**
- Water's high surface tension allows it to remain in a liquid state below its freezing point.
- Surface tension is the cohesive force between water molecules at the surface, which prevents them from escaping into vapor or freezing into ice.

3. **Lack of Nucleation Sites:**
- Nucleation sites are points where ice crystals can form.
- Supercooled water lacks sufficient nucleation sites to initiate ice crystal formation.
- Without nucleation sites, the water molecules remain in a liquid state despite being below the freezing point.

**Supercooling in Nature**

Supercooling of water can occur naturally under specific conditions, such as:

1. **Cold Clear Nights:**
- During cold, clear nights, when there is no disturbance or impurities in the water, supercooling can occur.
- The absence of impurities minimizes nucleation sites, allowing the water to remain in a liquid state.

2. **Rapid Cooling:**
- Rapid cooling can also contribute to supercooling.
- If water is cooled quickly, there might not be enough time for ice crystals to form.

**Conclusion**

While water usually freezes below zero degrees Celsius, it can supercool and remain in a liquid state under specific conditions. The high purity of water, its high surface tension, and the absence of nucleation sites are crucial factors in allowing water to supercool. This extraordinary property of water has been observed in nature during cold, clear nights, or when water is rapidly cooled.