But water may pool at {HEAD ~ the top end} of {TAIL ~ the array}, and on structures such as rooftops, the pooling may have undesirable consequences 
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But water may pool at { HEAD ~ the top end } of { TAIL ~ the array } , and on structures such as rooftops , the pooling may have undesirable consequences
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH