What is a nanometer, how small is it and can it be used to clean polluted water?

I believe there are 1 Billion Nanometers in a Meter. Don't know how it will clean water? Curious.

So you are asking about a filter which filters down to a nanometer, right? The smallest filter I have heard about takes out pollutants as small as 200 nanometer. Most germs are 1000 nanometers in size. You can not see a nanometer with the nakes eye, you need a micron microscope.

You can make the relationship between nano and nine, for nine zeroes.

nano = \frac{1}{1,000,000,000}

There are 9 zeroes as you can see :)