成功的微生物控制计划的要素包括源头保护、处理、消毒和分配系统的运行和维护。虽然每个单独屏障的重要性都很明显，但直到地表水处理规则（SWTR）的引入，多重屏障的概念才正式确立。SWTR于1989年6月最终确定，并于1993年6月生效。如本文所示，该规则正式确立了微生物控制的多重屏障概念，包括: 源头保护，减少细菌和病毒的风险；通过混凝和过滤去除；一次消毒，以杀死或灭活可能通过处理厂的微生物；以及配送系统的维护或微生物控制。到目前为止，主要的重点是治疗和消毒。然而，最近，电源保护开始受到一些关注，而配电系统的作用仍然没有得到同样程度的关注。随着即将到来的消毒剂/消毒- 产品（D/DBP）规则我们希望看到通过膜过滤生产出高质量的水。然而，在许多情况下，这些水仍将排入旧的/不完善的分配系统。例如，其中一些系统有100多年的历史，带有钢或铸铁管道和大量的死端。另一些储罐根据系统能量等级线/水力锁定，导致储罐内部积水和生物膜生长。这些系统中的大多数都是为适应火灾流量而设计的，在某些情况下，季节性需求可能会导致管道和存储空间过大，很少使用。 关于这些系统仍然可以确定的是，它们的设计并没有考虑到水质，也没有考虑它们可能对水质造成的影响。本文讨论了更严格的饮用水法规，以及与陈旧或低效的配水系统相关的水质问题。作者提供了几种积极的解决方案来处理这些问题，并指出了在处理这些问题时可能出现的一些困难。

The elements of a successful microbial control program consist of source protection, treatment, disinfection, and distribution system operation and maintenance. While the importance of each of these individual barriers is clear, it wasn't until the introduction of the Surface Water Treatment Rule (SWTR) that the concept of multiple barriers was formally established. The SWTR was finalized in June 1989 and became effective in June of 1993. As illustrated in this paper, this rule formally established a Multiple Barrier Concept for microbial control that includes: source protection to reduce the risks of bacteria and viruses; removal by coagulation and filtration; primary disinfection to kill or inactivate the microorganisms that might pass through the treatment plant; and maintenance or microbial control in the distribution system. To date the primary focus has been directed towards treatment and disinfection. More recently, however, source protection has begun to gain some attention while the role of distribution systems is still not receiving the same level of attention. With the upcoming Disinfectant/Disinfection By-Product (D/DBP) Rule we expect to see the production of very high quality water, produced in some cases by membrane filtration. However, in many cases this water will still be discharged into old/inadequate distribution systems. Some of these systems for example are over 100 years old with steel or cast iron piping and a large number of dead ends. Other have storage tanks that are locked out based on system energy grade line/hydraulics resulting in stagnant water and biofilm growth on the tanks' interior. Most of these systems were designed to accommodate fire flows and in some instances seasonal demands as a result may have oversized pipes and storage that is rarely used. What remains certain about these systems is that they were not designed with water quality in mind and little consideration has been given to what impacts on water quality they may have. This paper discusses the more stringent drinking water regulations and the water quality problems associated with antiquated or inefficient distribution systems. The authors offer several proactive solutions for dealing with these issues and point out some difficulties that may arise when dealing with these problems.