Step 1: Think about what actually happens to water in nature.
As water moves through soil, wetlands, and water bodies, it passes through layers of sediment, gets broken down by microorganisms, and cycles through evaporation and rainfall.
Step 2: Identify who or what is doing this work.
None of this filtering and cleaning is done by machines, humans alone, or chemicals alone - it happens through the ordinary functioning of the ecosystem itself.
Step 3: Name the responsible mechanism.
This natural filtering, carried out by soil, microbes, and the water cycle together, is what we call ecosystem processes.
\[ \boxed{\text{Ecosystem processes}} \]