  We present a line survey of the ultra-luminous infrared galaxy Arp 220, taken
with the newly installed SEPIA Band 5 instrument on APEX. We illustrate the
capacity of SEPIA to detect the 183.3 GHz H2O 31,3-22,0 line against the
atmospheric H2O absorption feature. We confirm the previous detection of the
HCN(2-1) line, and detect new transitions of standard dense gas tracers such as
HNC(2-1), HCO+(2-1), CS(4-3), C34S(4-3), HC3N(20-19). We also detect HCN(2-1)
v2=1 and the 193.5 GHz methanol (4-3) group for the first time. The absence of
time variations in the megamaser water line compared to previous observations
seems to rule out an AGN nuclear origin for the line. It could, on the
contrary, favor a thermal origin instead, but also possibly be a sign that the
megamaser emission is associated with star-forming cores washed-out in the
beam. We finally discuss how the new transitions of HCN, HNC, HCO+ refine our
knowledge of the ISM physical conditions in Arp 220.
