The first thing we had to do with the sample was to extract the DNA present in the water in a pure form for the PCR.
We did that with a Qiagen DNeasy PowerWater Kit.
As you would expect, this consists of a purification procedure with several steps.
In each step we take a physical or chemical action on the sample, which splits it into two parts: the one with the DNA and the one without.
We then take the part with the DNA, and throw away the one without the DNA.
The first steps are coarser, and finer and finer splits are done as we move forward.