Feddersen (F/43 no year) has a tracing board which he says is a French board for the 5th degree of the Ancient and Accepted Scottish Rite. Besides the well, the board also features the Vessel with Rams.
The short French ritual “Les Antipodiens” (see gun) has an explanation for the well:
The well means that when the brethern finished their labors, they were sanctified.
A 29th degree Ancient and Accepted Scottish Rite tracing board speaks of: “a well for purification”.
On a French tracing board in Les Francs Maçons Écrasés (1747) a tracing board is described as containing two “lavoirs”, ‘washing places’. See wheelbarrow (the two dark spots left and right of the mosaic pavements are the “lavoirs”).
I can imagine the fountain having a similar symbolism.
Top: Dąbrowski P. 212. Year and designer unknown.
Bottom: Feddersen (Die Arbeitstafel in der Freimaurerei Band I (1982) F/43, P. 313) gives as source Maurerisches Handbuch, 1829 (first edition 1821, this is a translation of Manuel Maconnique Ou Tuileur De Tous Les Rites De Maconnerie Pratiques En France by C. Vuillaume, 1820)