Arrow points to Flow Control Valve which allows pressure in the E61 group head to be adjusted. To plumb in to a water supply you'd need to have a rotary pump instead of a vibration pump (solenoid operated). This is the domain of dual boiler machines which mine isn't. Dual boilers machines cost alot more and could require a separate GPO power supply as 2 boilers in operation from cold could need 15A instead of a 10A circuit. The Profitec 500 is one of the larger single boiler (heat exchanger machines) and boiler design allows pulling water and steam together.
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Explanation here:
Whole Latte Love and Profitec/ECM Launch Flow Control Device for E61 Groupheads
I bought my setup from Jetblack Espresso at French's Forest (head office). They also have outlets in Newcastle, Kiama, Hobart, Brisbane and Melbourne. If on Sth side of Sydney Di Pacci are very good.
Another in Melbourne who offered advice online (I am a member of Coffeesnobs) knowing he would not get a sale is Chris at
talkcoffee.com.au. Top fella. Tell them I sent you, I might get a bag of beans.

All these outlets sell Fiorenzato grinders as well as a number of less and some much more expensive grinders.
I have looked longingly at coffee machines for decades and decided if I didn't scratch the itch now I might never get one. This is a setup I can leave in my will to my son, and with the right maintenance he could do the same for his if he ever gets motivated.