Does Building Age Affect Water Use? Size and Age Measured Across 58,750 Buildings

The question this answers

Building water benchmarks are almost always published by building type. Type matters, and we have published that table separately. But two other variables are available in the same disclosure data and are rarely reported: floor area and year of construction. Both turn out to predict intensity, and both point the same way.

This analysis covers 58,750 building-years with usable water, floor area and construction-year data from New York City Local Law 84 disclosure filings.

Bigger buildings use less per square foot

Restricting to multifamily housing, which is the largest single category at 40,800 building-years and removes the confounding effect of building use, intensity falls steadily with size above 50,000 square feet.

Building size	Building-years	Median gal/sq ft/yr
Under 25,000 sq ft	113	56.8
25,000 to 50,000 sq ft	15,550	65.4
50,000 to 100,000 sq ft	14,270	54.3
100,000 to 250,000 sq ft	7,978	40.5
Over 250,000 sq ft	2,889	36.7

Source: NYC Local Law 84 disclosure filings, multifamily housing only. Medians calculated by The Plumbing Brief.

What this means. A multifamily building over 250,000 square feet uses 44 percent less water per square foot than one of 25,000 to 50,000. The likely mechanism is occupant density per square foot rather than efficiency: larger buildings in New York tend to have more common and circulation area per resident, which dilutes fixture-driven consumption across more floor space. This data cannot confirm that mechanism, because it holds no occupancy counts.

The under 25,000 square foot band breaks the pattern at 56.8, but it rests on only 113 building-years and should not be cited as a trend point.

Newer buildings use less, in every era step

Construction era	All types, building-years	All types median	Multifamily median
Before 1930	22,133	48.1	65.1
1930 to 1949	10,157	48.2	57.3
1950 to 1969	10,623	39.5	47.4
1970 to 1989	4,631	36.6	46.0
1990 to 2009	6,321	36.6	42.8
2010 or later	4,950	32.0	35.1

Source: NYC Local Law 84 disclosure filings. Medians calculated by The Plumbing Brief.

What this means. Multifamily intensity falls at every era step without exception, from 65.1 gallons per square foot for pre-1930 stock to 35.1 for buildings completed since 2010. That is a 46 percent reduction across the age range. The all-types series falls too, though it plateaus between 1970 and 2009 at 36.6 before dropping again.

The era pattern is consistent with federal fixture standards, which took effect in 1994 and set toilets at 1.6 gallons per flush and showerheads at 2.5 gallons per minute. It is also consistent with simple fixture replacement in newer stock. This data cannot separate the two.

The evidence

1. Usable building-years with water, floor area and construction year: 58,750. Source: NYC Local Law 84 filings, retrieved 2 October 2026.
2. Multifamily building-years analysed: 40,800, median 52.2 gallons per square foot per year. Source: NYC Local Law 84.
3. Multifamily over 250,000 sq ft: 36.7 gal/sq ft. Source: NYC Local Law 84.
4. Multifamily 25,000 to 50,000 sq ft: 65.4 gal/sq ft. Source: NYC Local Law 84.
5. Difference between those bands: 44 percent lower in the largest band. Source: calculated by The Plumbing Brief.
6. All types, built before 1930: 48.1 gal/sq ft across 22,133 building-years. Source: NYC Local Law 84.
7. All types, built 2010 or later: 32.0 gal/sq ft across 4,950 building-years. Source: NYC Local Law 84.
8. Multifamily before 1930: 65.1. Multifamily 2010 or later: 35.1, a reduction of 46 percent. Source: NYC Local Law 84.
9. Pearson correlation between year built and water intensity across 58,750 records: minus 0.119. Source: calculated by The Plumbing Brief.
10. Federal fixture standards effective 1994: toilets 1.6 gallons per flush, showerheads 2.5 gallons per minute. Source: Energy Policy Act of 1992.
11. Pre-1930 stock is the single largest era group in the dataset at 22,133 building-years, or 37.7 percent. Source: NYC Local Law 84.
12. Only 91 of 58,102 buildings reporting both figures record any outdoor water use, so indoor and total water are effectively identical in this dataset. Source: calculated from NYC Local Law 84.

What the numbers imply

Size explains more than era, within multifamily

Formula. Spread between highest and lowest band median, compared across the two dimensions, within multifamily housing only.

Calculation. Size spread: 65.4 down to 36.7, a range of 28.7 gallons. Era spread: 65.1 down to 35.1, a range of 30.0 gallons.

Finding. The two dimensions produce almost the same spread, 28.7 against 30.0 gallons per square foot. Neither dominates. A benchmark that controls only for building type is leaving roughly 30 gallons per square foot of explainable variation on the table in each direction.

Limitations. Size and era are correlated in New York, because the pre-war stock skews to particular size bands. These are unadjusted marginal medians, not a regression, and the two effects are not separated here.

The correlation is weak even though the pattern is consistent

Formula. Pearson correlation between year of construction and water intensity across all usable records.

Calculation. r equals minus 0.119 across 58,750 records.

Finding. The direction is consistent and the band medians fall monotonically for multifamily, but the correlation is weak. Construction era shifts the centre of the distribution without determining any individual building’s consumption.

Limitations. A weak linear correlation is expected when the relationship is step-like rather than linear and when within-band variation is large. The band medians are the more informative statistic here, and the correlation is reported to prevent the band pattern being overread.

Indoor and total water are the same number in this dataset

Formula. Share of buildings where total water exceeds indoor water by more than 0.5 percent.

Calculation. 91 of 58,102 buildings reporting both, or 0.2 percent.

Finding. Outdoor water use is effectively unreported in this dataset. Anyone using these filings can treat indoor and total water as interchangeable, which is not true of datasets covering lower-density regions where irrigation is material.

Limitations. This is a reporting observation, not a statement that New York buildings have no outdoor water use. Owners may not meter or report it separately.

Download the data

Both breakdowns are published as a CSV under a Creative Commons Attribution 4.0 licence. Attribution: The Plumbing Brief. Building age also shapes heating choices, a factor worth weighing alongside radiant floor heating costs when planning renovations.

Water intensity by size band and construction era (CSV)

How this report was built

Methodology

Source. All 103,259 New York City Local Law 84 disclosure filings, retrieved through the NYC Open Data API.

Cleaning rules. A filing was included where reported water use exceeded zero, gross floor area was at least 1,000 square feet, and calculated intensity fell at or below 500 gallons per square foot per year. Construction-era analysis additionally required a year built between 1850 and 2027. That left 58,750 usable building-years.

Why multifamily for the size analysis. Restricting to one building type removes building use as a confounder, and multifamily is the largest category at 40,800 building-years. Size bands with fewer than 30 building-years are not reported.

Unit conversion. Reported water use is in thousands of gallons and was multiplied by 1,000. The conversion was validated separately against the federal CBECS warehouse figure, which agrees within 6 percent.

Statistic used. Median throughout, because every band contains high-consumption outliers.

Retrieval date. 2 October 2026.

Data limitations

• New York City only. Climate, density, building age profile and water pricing all differ elsewhere. Do not cite these as US benchmarks.
• Local Law 84 covers buildings above the disclosure threshold. Small buildings are absent, which is why the under 25,000 square foot band holds only 113 building-years.
• Filings are self-reported and some values are estimated rather than metered.
• Size and construction era are correlated in this stock. The two effects are not separated, and no regression is performed.
• No occupancy data is available, so intensity per person cannot be calculated. The density explanation for the size effect is plausible but untested here.
• The unit is building-years, not distinct buildings. A building appearing in several reporting years is counted once per year.
• The all-types era series mixes building uses, so part of its movement reflects which uses were built in which era.

Source quality ranking

Tier 1. New York City Local Law 84 disclosure filings via NYC Open Data. Energy Policy Act of 1992 for fixture standards.

Tier 2. US EIA Commercial Buildings Energy Consumption Survey, 2012, used only for the conversion validation referenced above.

Tier 3. None used.

Excluded. Vendor benchmarking figures and any building water intensity figure published without a stated floor area denominator.

Figures worth quoting

• Multifamily buildings over 250,000 square feet use 44 percent less water per square foot than those of 25,000 to 50,000.
• Multifamily stock built since 2010 uses 46 percent less water per square foot than pre-1930 stock.
• Multifamily intensity falls at every construction-era step without exception.
• Size and age each explain about 30 gallons per square foot of spread, roughly the same amount.
• Only 0.2 percent of these buildings report any outdoor water use at all.

Briefing note

Building size and construction era each predict water use per square foot about as strongly as each other, according to an analysis of 58,750 building-years of New York City Local Law 84 disclosure filings. Within multifamily housing, buildings over 250,000 square feet record a median 36.7 gallons per square foot per year against 65.4 for buildings of 25,000 to 50,000 square feet, a difference of 44 percent. Across construction eras, multifamily intensity falls at every step from 65.1 gallons for pre-1930 stock to 35.1 for buildings completed since 2010, a reduction of 46 percent. The era pattern is consistent with federal fixture standards effective in 1994, though this data cannot separate that from ordinary fixture replacement. The correlation between year built and intensity is weak at minus 0.119, so era shifts the distribution without determining any individual building.

How reporters could frame this

1. Big buildings use far less water per square foot than mid-sized ones
2. Every decade of construction since 1930 uses less water than the one before
3. Pre-war apartment buildings use nearly twice the water of post-2010 stock
4. Building water benchmarks ignore the two variables that matter most
5. Why a per-square-foot water target is the wrong target

Related questions

Do bigger buildings use more water? More in total, but substantially less per square foot. Multifamily buildings over 250,000 square feet use 36.7 gallons per square foot against 65.4 for those of 25,000 to 50,000.

Do older buildings use more water? Yes. Multifamily stock built before 1930 records 65.1 gallons per square foot against 35.1 for stock built since 2010.

Why do older buildings use more? The pattern is consistent with federal fixture standards effective in 1994 and with fixture replacement in newer stock. This data cannot separate those explanations.

How much does construction era change water use? About 30 gallons per square foot per year across the full age range in multifamily housing, a reduction of 46 percent.

Is the relationship between age and water use strong? The direction is consistent but the correlation is weak at minus 0.119. Era moves the centre of the distribution rather than determining individual buildings.

What about building type? Type matters too and is published separately in our building water intensity table covering 44 types.

Does outdoor water use affect these figures? Barely. Only 91 of 58,102 buildings reporting both figures record any outdoor use, so indoor and total water are effectively identical here.

Can I use these numbers outside New York? Not as absolute benchmarks. Use the relative pattern between size bands and eras, not the gallon values.

Why use the median rather than the average? Because every band contains high-consumption outliers that pull means well above medians.

How reliable is self-reported disclosure data? It is a regulatory filing with its own quality-alert fields, and some values are estimated. The unit conversion used here was validated against the independent federal CBECS warehouse figure to within 6 percent.

How to cite this report

The Plumbing Brief, “Does Building Age Affect Water Use? Size and Age Measured Across 58,750 Buildings”, https://theplumbingbrief.com/does-building-age-affect-water-use/, accessed [date].

Last reviewed: 2026-10-02.