Riverside Teahouse Water Well (spoiler)

[Gaindalf the Whey]

The well you can interact with and drink from gives the refreshed buff which gives +10hp until the next long rest.

Does anyone know if there's a cap to how many times you can use this after long rests? Could I take it after every long rest?

[bf1tz.psu]

afaik yes. however, there appears to be a bug where only your party members get the buff. Also, if you anger the hag whilst using the buff, it's not pretty.

[bullse]

There is no cap but as indicated, once you do certain things (progressions) pertaining to the Hag, the well becomes useless.