Orion ,
 I haven’t come across a pic of water tank/tower in that area between the monument and Stonehenge Bottom , it’s not in view in the classic 30’s pic from Stonehenge bottom (“fork left for Exeter “ and AA box ) .
There are a number marked on various plans and maps and I thought the closest to the monument was at the pig farm established for a short while in 20s . The presence of the these tanks /towers certainly indicate a lack of viable water courses on the chalk in that area .

George