IAPMO Water Demand Calculator

We did the math: correctly sized plumbing pipes reduce construction costs and address water aging

The IAPMO Water Demand Calculator is available from the Apple App Store for Apple devices and Google Play for Android devices.

Plumbing systems in new home construction are routinely overbuilt, increasing housing costs because the most commonly-used pipe sizing formula is almost 90 years old – developed well before today’s innovative low-flow fixtures and appliances came on the scene.

Using the IAPMO Water Demand Calculator for new residential construction significantly reduces water aging, delivers hot water faster, generates significant construction cost savings, reduces the carbon footprint of the structure, and subsequently saves on water- and water heating-related energy utility bills for the entire life of the plumbing system.

Unnecessary New Home Construction Costs From Outdated Pipe Sizing


home meter connections

UP TO $250 per year

in water and sewer charges

UP TO $2,500

more in piping costs per home

Savings in New Home Construction From Proper Pipe Sizing

Single-family Home

The total average savings for a typical single-family home can exceed $2,000 and can be as high as $5,000, depending on location.

45-unit Multi-family Building

The potential savings are even higher and can exceed $100,000 on a 45-unit multi-family building, especially where utility meter connection fees are high due to water scarcity.

200-unit High Rise Apartment

Could see about $250,000 in water plumbing system construction savings, while the owner could save over $10,000 per year in water and sewer charges.

Excessive construction and meter connection costs are just the beginning. Oversized pipes just don’t work as well with today’s high-efficiency fixtures and appliances.

Hot water taking too long to get to your shower? Large-volume pipe diameters cause hot water delivery delays to low-flow fixtures. Even worse are the risks of water-borne pathogens from water aging and stagnation in oversized residential water pipes.

Problems With Outdated Pipe Sizing


increase the wait time for hot water to arrive at your faucet or shower


increases the risk of bacterial growth which can lead to diseases like Legionnaire’s Disease (Legionella Pneumophila)


for homebuilders and consumers

The IAPMO Water Demand Calculator accurately predicts peak water demand in single-family homes and apartment buildings, reducing the carbon footprint of the structure and saving consumers on both their water and water heating-related energy utility bills for the entire life of the plumbing system.

Benefits of Proper Pipe Sizing


Improved water conservation and energy use


Improved housing affordability with reduced cost of building materials and meter fees


Improved water quality and public health

We Invest in Plumbing Science

IAPMO provides the Water Demand Calculator as a free app for Apple and Android to facilitate rapid adoption and improve new home plumbing systems for everyone.

IAPMO continually invests in plumbing science to help communities benefit from today’s sophisticated water-related technologies in our homes and buildings. It’s one of the ways we play a vital public health role in assuring access to clean water and sanitation.

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