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I am searching for more knowledge as to what limitations were placed upon delivery to in-house water supply systems during the Roman Era. These limitations could have been via code, pipe size, pipe length, use or limit of expanders (sections of pipe that rapidly increase in diameter to increase flow-rate).

The central cistern / main pressure pipe (name?) was tapped and pipes moved water to the affluent households. At some point water theft became a significant issue and laws were enacted to prevent 'taking too much'. This was during the Roman era, in an unknown region.

The use of an expander nozzle attached directly to or close to a distribution reservoir, at high pressure, will cause an increased flow and negatively impact others tapped into the system.

At some point a water commissioner or other position decreed that some length of standardized pipe must be used prior to increasing the size of a pipe or expansion nozzle.

Roman water commissioner Julius Frontinus did speak about water piracy but I can only find references to tapping the aqueduct, not the sneakily use of different sized pipes to get better water pressure inside houses.

(Background: I believe I came across it in a Fluid Dynamics book for Chemical Engineering but am unable to locate any detail nor find the reference in my college books. I also studied Roman History and Latin for 6+ years and don't have it notated. )

It wasn't so much theft in household as 'pressure'. There's only so much of that to go around based on head and utilization of an expander lowers the available head for others. Can I get away with 'it's complicated'?

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    An article here has some on standardized taps used- the calix. Mentions Frontius and Vitruvius.
    – justCal
    Oct 1 at 12:40
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    @MCW I can do that- I wanted references because I wanted to read up on it! I only recall getting a page of material around it and it's bugged me for nearly 20 years I didn't learn more on it. I'll revise the title, remove the request for references- is 'authoritative texts' better to ask to be pointed towards?
    – J.Hirsch
    Oct 1 at 20:06
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    Superb - Upvote. looks good
    – MCW
    Oct 1 at 20:24
  • One guess is that water theft was not an issue at household. You can only use so much water for domestic service, so if you get enough it does not make sense to break the rules to get more. The things I have read about water theft from aqueducts link it to farmers diverting the water to water the crops, which required way more water than any household or even neighbourhood would use.
    – SJuan76
    Oct 1 at 22:25
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    @SJuan76, rather than as theft, think of it in terms of what happens when you flush the toilet and the water in the shower slows down. The question is about houses that are connected so that they act like the toilet, taking all the water they want and making the other houses have to put up with very slowly running taps. Oct 2 at 0:30
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The details from the question align with those found in the report by Roman water commissioner (and former general) Sextus Iulius Frontinus, De Aquis, ca. 100 AD. Here are the relevant sections from the second volume of the publication, taken from the English translation by Charles E. Bennett in the Loeb edition of 1925 as found online at LacusCurtius:

[105] [...] Neither must the deputy permit the free option of connecting directly to the ajutages any sort of lead pipe, but there must rather be attached for a length of fifty feet one of the same interior area as that which the ajutage has been certified to have, as has been ordained by a vote of the Senate which follows:

[106] The consuls, Quintus Aelius Tubero and Paulus Fabius Maximus, having made a report that some private parties take water directly from the public conduits, and having inquired of the Senate what it would please to order upon the subject, it has been resolved that it is the sense of this body: [...] and no one of those to whom a right to draw water from the public conduits has been granted shall have the right to use a larger pipe than a quinaria​ for a space of fifty feet from the reservoir out of which he is to draw the water. [...]

[112] In some of the reservoirs, though their ajutages were stamped in conformity with their lawful admeasurements, pipes of a greater diameter [than the ajutages] were at once attached to them. As a consequence, the water not being held together for the lawful distance,​ and being on the contrary forced through the short restricted distance,​ easily filled the adjoining larger pipes. Care should therefore be taken, as often as an ajutage is stamped, to stamp also the adjoining pipe over the length which we stated was prescribed by the resolution of the Senate.

Paullus Fabius Maximus and Quintus Aelius Tubero held the consulship in 11 BC. As already alluded to in the question, the issue of some water users gaining an unfair advantage by installing a wide-diameter pipe directly after the calibrated outflow of neighborhood storage tanks was addressed by a directive passed by the Roman Senate that limited the diameter of the first fifty feet of pipe after the outflow from the tank to a maximum of about 0.9 inch (= 2.3 cm). This numerical value is derived from section 25 in the first volume:

The most probable explanation is that the quinaria​ received its name from having a diameter of 5⁄4 of a digit

where a Roman digit is equal to 18.5mm according to Wikipedia

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  • BINGO! "to use a larger pipe than a quinaria​ for a space of fifty feet" There we go- that popped the memory! That's the text I recall seeing. I have a lot of reading to do. Thank you!
    – J.Hirsch
    Oct 18 at 15:26

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