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So don't worry so much about how to use  had had  as a unit of grammar, they will come together naturally when you want to express the verb ' to have ' in the past perfect. Let's consider a different verb for a moment like  to want .
had has have been is usually used for something that was done in the past and still applies multiple events was were usually applies to something done in the past that no longer applies single eventexample the well had been producing clean water the well was producing clean waterad has have been is usually used for something that was done in the past and still applies multiple events was were usually applies to something done in the past that no longer applies single event example