The first person to examine pool water under a microscope was Leeuwenhoek. Using microscopes he crafted himself, he observed tiny, constantly moving creatures teeming in the water. This discovery marked one of the earliest significant observations of microorganisms.

Robert Hooke first discovered the cell in 1665 by examining a slice of cork. This groundbreaking discovery paved the way for microscopic investigations and provided a scientific foundation for Leeuwenhoek's subsequent observations of living organisms in pool water. Leeuwenhoek built upon Hooke's pioneering work by applying microscopy to a different domain.

Leeuwenhoek was a scientist who enjoyed grinding lenses in his spare time. He constructed his own microscopes using high-quality lenses that he personally crafted. It was through these custom-made microscopes that he was able to observe the microscopic life in pool water.

According to Schwann and Schleiden's cell theory, all living organisms are composed of one or more cells. Cells are considered the most basic structural and functional units of life. Furthermore, all cells arise from pre-existing cells through division.