educational estimating tool - not professional advice. every number here is a placeholder until verified. read the full disclaimer.
what one more bathroom does to a water service
water service is sized in steps, not by the fixture. this page adds up a small project's fixture units, shows which meter and service size it lands on, and draws where the next step is - and what one more bathroom or one more unit does to it.
who this applies to. the step prices here come from UPC table 610.4, which sizes service for buildings of three or more units and for commercial buildings. for a single house, a duplex or a townhome, austin sizes the meter from its own table 610.1 instead, where three bathrooms or fewer is a 5/8 inch meter - so on one house, an added bathroom crosses nothing in austin. the meter size shown below is the multi-unit table 610.4 answer, not austin's answer for a house. this page shows how a service step is priced, not what a bedroom costs on a house.
the step that started this page
Utility capacity is a real threshold problem in Austin infill, and it is a fixed-size one: one added bathroom can push a small multi-unit or commercial project past a service-line capacity limit, and the fix is a full utility line upsize from the site back to the street - one panelist's example put it in the six figures*, enough on its own to kill a small project's pro forma. What follows is not one specific address; it is a worked reconstruction, built from this page's own tables, that lands at the same scale for the same reason - so the mechanism is checkable, not just asserted. It is a table 610.4 illustration: a single unit is used below because it keeps the arithmetic short, and in Austin a lone house would be sized from table 610.1 and would not cross this step.
A single small unit - one full bath, one kitchen sink, one dishwasher, one washer, one hose bibb - adds up to 17.0 WSFU, which is not a number this page chose to make a point: it is exactly the ceiling of a 3/4-inch meter on a 3/4-inch line in UPC Table 610.4, read in the 46-60 psi column at 100 ft. A house like that is already standing at the edge of its tap with room for nothing more. Add one more full bath's worth of fixtures - a bathroom or a bedroom with its own bath - and the total rises to 24.5 WSFU, past that ceiling and into the next band, which needs a full 1-inch service line. The meter can stay at 3/4 inch, but the existing tap is only a 3/4-inch line, so the site owes the same kind of line upsize: $8,000 for the band step (a placeholder - the meter itself does not change here) plus the line upsize itself*, site to street, for the identical mechanism - and that cost is whatever the utility quotes for the run. One scope limit, repeated because it matters: in Austin a one- or two-family dwelling or townhome has its meter sized by Austin's own table 610.1, not table 610.4 (see the meter sizing check below), so this reconstruction shows the table 610.4 mechanism, not Austin's answer for a single house.
This is already loaded below. The inputs are set to this single-unit example. Change extra full baths per unit from 0 to 1 and watch the "this project" row cross the line - that one field is the whole case study. The line upsize box starts empty: enter your utility's quote to see it in the totals.
* this page does not supply a line-upsize cost - it starts empty and is whatever your utility quotes. until a quote is entered, every total below leaves it out and says so. the WSFU-to-cost mapping below is this page's own placeholder, not a specific utility's quote - marked and treated as unverified everywhere it appears, including in the checks below.
the project
fixture unit values - edit to match the adopted table
| fixture | WSFU, private use | used for | status |
|---|---|---|---|
| bathtub or tub/shower combo | full bath, extra baths | verify | |
| shower stall | full bath, if chosen above | verify | |
| lavatory | every bath | verify | |
| water closet, flush tank | every bath | verify | |
| kitchen sink | per unit | verify | |
| dishwasher | per unit | verify | |
| clothes washer | per unit | verify | |
| hose bibb | per unitUPC counts each bibb after the first at 1.0 - not modeled, runs high | verify |
meter and service bands - edit to match the utility's letter
| meter | service line | up to (WSFU) | cost to step past this band ($) | status |
|---|---|---|---|---|
| 3/4 in | 3/4 in | verify | ||
| 3/4 in | 1 in | verify | ||
| 1 in | 1 in | verify | ||
| 1 in | 1-1/4 in | verify | ||
| 1 in | 1-1/2 in | verify | ||
| 1-1/2 in | 1-1/2 in | verify | ||
| 2 in | 2 in | verify |
the band limits are from the 2024 UPC table 610.4, 46-60 psi column at 100 ft of developed length (17 / 33 / 36 / 67 / 85 / 151 / 370). the table keeps only the rows where the meter and the line grow together and leaves out the mixed sizes the table also lists (3/4 in meter on a 1-1/4 in line at 39, 1-1/2 in meter on a 1-1/4 in line at 78, 1-1/2 in meter on a 2 in line at 318), so between 151 and 318 WSFU the table may allow a smaller meter than this page shows. Austin adopted the 2024 UPC (city code § 25-12-151), and these rows were checked against it. the step costs are assumptions: $8,000 for a 3/4 to 1 in meter step, reused for the three service-line-only steps; $35,000 for the 1 to 1-1/2 in meter step; $90,000 for 1-1/2 to 2 in. past the last band, or wherever the required service line is bigger than the existing one, the site-to-street line upsize above is added once you enter a quote.
where this project lands
| scenario | WSFU | meter / service | added cost |
|---|
checks - the numbers behind the claims
read this before using any of it
the cliff is real, and it is about capacity thresholds, not fixtures. a utility does not price the bathroom. it prices the meter and the pipe the bathroom pushes you onto, and those come in fixed sizes. the fixture that crosses the line pays for the whole step, and if the step is a bigger service line, the step runs from the meter box back to the main in the street.
find out before the unit mix is locked. the panel's example was one more bathroom's worth of fixtures. the cheapest question on a small infill project is a capacity read from the utility while the plan is still a sketch. after the pro forma is built around a bathroom count, the answer is either a redesign or a six-figure line item that was not in the budget.
the city is piloting early utility coordination. Austin is trying upfront coordination of water, electric, street trees, sidewalk and curb on its own capital street projects. it has not reached private residential permitting yet. until it does, the coordination is the project's job, and this page is a way to start the conversation with a number instead of a guess.