Yes, it is big enough for the NS adapter and the ordinary water tank that is already attached to the nanopresso. But if you mean the optional water tank the nanovessel, the assembled NS-Nanopresso-Nanovessel won't fit in the L case and is too big.
However, the L Case should fit the NS-Naopresso-Baristakit (I still have to find out when I get the Baristakit) because the L Case is too big for the NS Kit with Nanopresso only.