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Where does fixture-level greywater treatment start to pay off?
For a small building reusing greywater for non-potable uses, a shared treatment unit seems like it could keep the treatment hardware and servicing in one place. But if the shower, laundry, and intended reuse points are spread out, extra pipe runs and access work might eat into that saving.
Simpler treatment at individual fixtures could shorten some runs, though it may mean maintaining several units and limit which sources can serve which uses. How much do the number and location of greywater sources affect the installed and ongoing costs? And which treatment and maintenance requirements, or local code constraints, tend to decide between the layouts?
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Source count alone may be less decisive than how the sources and reuse points cluster: one shared unit can avoid duplicated equipment and servicing, but long or awkward routes may erase that advantage. Several nearby fixtures feeding nearby uses could make local units more attractive, though they multiply maintenance points. I’d compare actual pipe routes and access first, then check whether the treatment needed for the intended source-to-use pairing and local rules allow either layout.
For example, imagine the shower and laundry are together at one end of a small building, while the reuse points are far away. A shared unit near those sources might send treated water along one route to the distant uses; local units could shorten the runs to treatment, but wouldn’t remove the need to get water to those uses. The actual route and access for each layout would decide whether that difference is worthwhile.
Before pricing either layout, check which source-to-use pairings local rules permit and what treatment and maintenance those pairings require. If an intended use calls for a treatment setup that only one layout can accommodate, that could settle the choice before pipe length or unit count does. The applicable requirements depend on the locally adopted rules.
Your point about multiplying maintenance points would weigh heavily for me: I’d prefer one shared unit if it can be placed somewhere easy to reach for routine servicing. If it ended up awkward to access, though, fewer units might not mean an easier maintenance routine in practice.
Are the reuse destinations fixed, or could they shift to another suitable use? If they’re flexible, that may let the layout follow source-to-use pairings the local rules permit, rather than adding runs to preserve a preferred destination; if they’re fixed, those routes become part of the comparison from the start.
I wouldn’t assume flexibility automatically saves pipework: an alternative use helps only if it’s permitted and actually closer or easier to reach. Water still has to get from treatment to wherever it’s reused, so I’d compare the practical routes to likely alternatives, not just count how many destinations could shift.
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