If you have a second look CS place the source on the new building on the GM. And the description say : L’eau qui s’écoule sur la petite placette publique triangulaire située à l’angle de la rue du Delta et de la rue du Patinage à Forest provient de la source dite du Calvaire. That not indicate that the source is on the place you initialy put : https://osmlab.github.io/osm-deep-history/#/node/9438224964 (CS put it on the 61). 

ReflexCity put the spring based on a IGN map aound 1980. It's on contour of 30 M. So if you take a IGN map from today on background make the position near the V2 of the spring. 

The reason i created the note , is that 1 years ago i didn't find the spring (SC quest) ; so i make some research and at least 2 ground survey. The actual situation is there's a continuous flow from a culvert comming fro the new appartements. 

Position on v2 can maybe a little improved but unless you have access on the construction plan , it will be difficult and it's already an improvement.  

Also If you take the topographic map from  Vandermaelen (1846-1854) he also indicate the position of the spring near is v2 (see previous screenshot). 

So we have 3 documentary source (including witch one you refer) ; that indicate that the source was not on the V1.
