微生物定植和由此产生的高种群通常发生在分布系统内的保护性外壳或结节上或内部。这些结垢的形成受到管道内各种物理、化学和生物活动的影响，可通过扫描电子显微镜（SEM）进行现场检查。扫描电镜照片非常生动地显示了分布系统中微生物的存活及其在结节形成中的可能作用。包括13个参考文献、表格、图表。

Colonization of microorganisms and resultant high populations often occur on or within protective encrustations or tubercles inside a distribution system. Formation of these encrustations is affected by a variety of physical, chemical, and biological activities within the pipes, which can be examined in situ by scanning electron microscopy (SEM). SEM photographs demonstrate very graphically the survival of microorganisms in the distribution system and their possible role in tubercle formation. Includes 13 references, table, figures.