Here's why:

* Water molecules are incredibly tiny. They are about 0.27 nanometers in diameter.

* Cells are much larger, ranging in size from a few micrometers to a few centimeters.

To put this in perspective:

* A nanometer is one billionth of a meter.

* A micrometer is one millionth of a meter.

This means a cell can be thousands to millions of times larger than a single water molecule.