Didn't know it was Waltham, thought it was Lexington. But yes a lookup of the stats via bostonradio.org says the transmitter is at '411 Waverley Oaks Rd. Waltham, MA'
WWZN is in the Waverley Oaks Industrial Park on Route 60 in Waltham just west of Waverley Sq, Belmont. This is not the first time that flooding has taken the station off the air. I'm more sure of the month than the year of the last such event but I believe it was in October of 1993 or 1994. I live about two miles north of WWZN in Arlington Heights. I have lived here for more than 45 years. In that time, my basement has had serious water in it three times, the current time being #3. For me, this event, though quite unpleasant, is not quite as bad as the previous time, which, as I said, I believe was October of 1993 or 1994. At that time, IIRC, the station that is currently WWZN (I don't remember what the calls were then) was off the air for five days. There was major damage to the equipment. I believe that a 50 kW transmitter was totaled.
A small stream (probably Beaver Brook) adjoins the Industrial Park parking lot. The WWZN Tx building is between the lot and the stream. The ATU buildings, two or three of which are IN the parking lot (with the ground systems beneath the asphalt) are on concrete piers, which elevate them I'd guess four feet above the lot. Because of those piers, I suspect that the ATUs may have escaped damage. Why the Tx building, whose main bay must be at least 20' high, isn't similarly elevated, I don't understand. Seems as though it would have been possible to build an elevated platform for the equipment inside the building, although some major equipment, like a huge power transformer, may have had to stay on the ground outside. Although there is a backup Diesel generator, if the water took out that huge transformer, the station would likely be forced off the air. And you don't get replacements for transformers that large overnight.