Which method ( coagulant, trickling water through sand, carbon filtration, etc.) do you think works the best? Why?

compost can be added to topsoil as a:

pesticide

affects the water bodies: excessive use of fertilizers causes eutrophication. the fertilizers which are used on plants affect the quality of land on which it is used, further causing erosion of soil. the fertilizers used on plants contain harmful chemical fumes which affect the environment.

colors do exist. the color of the sky is actually violet; humans percieve the color of the sky as blue.