The gemmara concludes that halach l'moshe misinai teaches us that nisuch hamayim is all 7 days of sukkos.From Rosh hashanah we learnt that Nisuch hamayim is done so that Hash-m will give us a good judgemnet for the rain. Why doesn't R Eleizer use this as a proof that even though its not the zman of rain its OK to hint or even make a zecher as long as we don't ask explicitly.
Gary Schreiber, Chicago
Hello there and thanks for your wonderful question. The Gemara concludes that according to Rebbi Yehoshua, Nisuch ha'Mayim is seven days, although theoretically it should only be one day. The source for this is a Halacha l'Moshe mi'Sinai. A Halacha l'Moshe mi'Sinai is something that has no logical explanation to it. This means that according to Rebbi Yehoshua the logical explanation of Nisuch ha'Mayim for the sake of rain, applies only to the last day, while Nisuch during the rest of the days has no logical explanation to it, unlike the Mitzvah of Lulav which is an explicit Torah obligation from the beginning of Succos, thus logic may also be applied to it.
P.S. I'm really sorry this question took so long to answer. Please be Mochel.
Thanks but doesn't the gemmara in RH say that nisuch hamayim B'CHAG (not lachar or bsof)is to obtain a favorable judgement. As long as it is done anytime during the chag it would be a siman kllalah. After I posed the question I did notice that the gemmara in RH is accoding to R Akiva(at least that's what I recall at this moment) who also is a bar plugta in Taanis. Perhaps the explanation lies there.
I think you answered your own question. According to other Tanoim there is logic to the days of the Nisuch and thus connection to water. The only exception to this is R' Eliezer who maintains that the Nisuch during the entire Chag is a Halacha l'Moshe mi'Sinai, thus we do not search for a logical explanation.
All the best.