Section 27-2031. Supply of hot water; when required

Except as otherwise
  provided in this article, every bath, shower, washbasin and sink in  any
  dwelling  unit  in  a multiple dwelling or tenant-occupied one-family or
  two-family dwelling shall be supplied at all times between the hours  of
  six  a. m. and midnight with hot water at a constant minimum temperature
  of one hundred twenty degrees Fahrenheit from a central source of supply
  constructed in accordance with the provisions of the building  code  and
  the  regulations  of  the  department,  provided  however that baths and
  showers equipped  with  balanced-pressure  mixing  valves,  thermostatic
  mixing  valves or combination pressure balancing/thermostatic valves may
  produce a discharge temperature less than  one  hundred  twenty  degrees
  Fahrenheit but in no event less than one hundred ten degrees Fahrenheit.
  Gas  or  electric  water  heaters may, if approved by the department, be
  utilized in lieu of a central source of supply  of  hot  water  if  such
  heaters:
    (1)   are  lawfully  in  use  on  July  fourteenth,  nineteen  hundred
  sixty-seven; or
    (2) are approved by the appropriate city agencies having  jurisdiction
  and  are  installed  in  a  structure  or  building  erected, converted,
  substantially  rehabilitated,   or   completely   vacated   after   July
  fourteenth, nineteen hundred sixty-seven.