In parshat Netzavim it says "from the wood choppers till the water cariers" I was wondering why was the word "Ad" used. Normaly it is used to show a wide spectrum of people. ( for example in parshat Bo: "from the bechor of paroh ro the bechor of a capive") Why is the word "Ad" used in parshat Netzavim?

Correct, a wide spectrum is the normal usage. The Seforno points out another exception, Shmuel I 15;3. There also we are referring to the entire nation (of Amalek) from man to (v'ad) woman from child to suckling, from ox to sheep, from camel to donkey. Within the greater context each v'ad entails the entirety of a subcategory. That would work here meaning the entirety of the category of menial workers. The Netziov contends the wood chopping is the most demanding of domestic tasks, while carrying water is the easiest. Hence the "ad" includes a wide spectrum of menial laborers.