Ive just completed the water treatment mission for the robots at greygarden...this was done at the same time where i had to select which faction to side with to create the teleporter. Upon completing the greygarden water treatment mission i had to go back to preston garvey, but when i spoke to him, there was no speech option to enable me to finish the treatment quest...instead it just assumed i wanted to side with the minutemen to build the teleporter...something which i wasnt ready to decide on yet.

Kind of annoying that there was no option to speak with him about the water treatment mission because until i finish this teleporter bit, theres no way for me to finish the quest.

Hope this helps...and it made sense...still not awake enough for legible conversation but felt i had to share with the devs.

Looks like youll have to make sure youve finished the water treatment level before going into the molecular quest.