Another excellent find from the “A Day in Pompeii” exhibit at the Denver Museum of Nature and Science — a water bypass box with valves:
As was the case for all Roman plumbing (the source of the name, actually), this was built of lead. Not a good thing over the long term, but likely not the worst health threat of the time. And given the metallurgical technology the Romans had on hand, lead was probably the only material they could have built something like this from.
From the placard:
Water flowing into this junction box through a lead pipe was diverted into one pipe at the top and two at the bottom. The top pipe may have carried water to the house, while the lower ones may have serviced the garden.