If you used water from a swimming pool, you probably got many bacteria per drop and it is likely the plate was covered and could not be counted. If you got so many colonies that they ran together, then your count is not accurate because they are hard to count and very likely some colonies consisted of 2 or 3 bacteria landing so close together that they grew as a single colony. Therefore, you may consider buying some test tubes and pipets as they are not so expensive. You can use small glass bottles, or other convenient vessels and count drops to make serial dilutions. You could put 49 drops of DF in a container and add one drop of well water, mix by swrilling and plate one drop.
Most foods sink in water, which means they are a little heavier than water.
Put this hard stuff in a separate section and subpages. It is also true that all killing and growth in bacteria cultures follows a logarithmic function, not a linear function. If those words are new to you, you have not completed a good algebra course. Do not fear this page and its subpages will teach you all you need to know. This page is a remarkable opportunity for you to learn some very interesting mathematics and biology.