Sentence:  In a WFI system, usually a distilled water loop, warm standing water can occur in <WSD>dead-legs</WSD> which are defined as dead-ends more than 5 to 6 pipe widths in length, and which extend downward, either straight or at an angle, from the loop. 
Meaning of the word marked with <WSD> tags:  (deadleg) (pipe with no outflow)