Water defines how people live, from showers to faucets to humidifiers humming in winter. While outdoor watering often gets the spotlight, indoor habits make a huge difference.

A new study published in the journal Earth’s Future explores how families across the United States consume water inside their homes, highlighting not just the obvious culprits but also the overlooked ones.

Data from 26,000 homes

The researchers analyzed more than 26,000 single-family homes across 39 major cities. Unlike previous studies, this one focused purely on indoor use with high-resolution smart meter data.

Landon Marston of Virginia Tech explained the significance of the study. “We didn’t have a great understanding of how much water was being used or how it was being used inside homes,” said Marston. “So, we kind of relied on these crude estimates to pinpoint that, and it’s not that precise.”

The smart sensors, developed by Flume, capture water flow every few seconds and use machine learning to determine which fixture or appliance is responsible.

Winter patterns in showers

The team studied December and January to avoid confusing outdoor watering with indoor use. Cold months reduce irrigation, making the classification more reliable.

The researchers noted that focusing on winter minimized seasonal noise, giving them a clearer view of how people use water inside their homes. By removing outdoor watering from the picture, the data better captured everyday activities such as toilet flushing, showering, and running appliances.

This seasonal focus also showed how weather influences behavior: colder days often led to longer showers, while drier conditions increased reliance on humidifiers.

Comparing households across regions during the same period created consistent conditions, making the findings more accurate and easier to interpret.

Toilet and shower use

Cities fell into three groups: high, medium, and low water users. Las Vegas, Phoenix, and Tampa topped the list for high use, while all six of the lowest were in coastal California.

The researchers linked California’s low usage to strict efficiency regulations and older housing stock. In contrast, high-use cities were often colder and drier, where residents relied more on humidifiers.

“What was really a driving factor was toilet events and showers,” said Marston. “We now look at this across the nation and find a similar pattern. That’s really a driving force.”

Toilets consumed about 40 percent of indoor water. Showers followed closely with around 30 percent. A detailed analysis revealed that high-use cities not only flushed more often but also used more water per flush and had longer, more frequent showers.

Other factors influencing water use

Yunus Naseri, lead author of the study, emphasized where conservation should begin. “Conservation efforts focused on reducing indoor residential water use can be most effective if they target these two end uses,” he said.

Yet toilets and showers are not the only contributors. Appliances like humidifiers and reverse osmosis systems increased usage in high-demand cities. Bathtubs and evaporative coolers also added to totals.

Older homes, surprisingly, were linked to lower water use than newer ones, possibly due to retrofitted fixtures or smaller household sizes.

Environment and water use

Weather shaped habits too. Colder temperatures correlated with longer showers and more frequent flushing, likely due to increased time spent indoors.

Wetter climates tended to use less water, while dry conditions encouraged humidifier use. These findings show how behavior adapts to environment, layering onto technology and policy.

The clustering of low-use cities in California highlights the power of state-level rules. Regulations requiring efficient toilets and showerheads, along with rebate programs and public campaigns, appear to have lasting effects.

The study suggests that combining efficiency standards with educational outreach could help other states achieve similar reductions.

Study limitations and future directions

The researchers caution that the dataset comes from self-selected households who purchased sensors, sometimes with rebates.

These households may already be more conscious of their usage, potentially biasing results. Still, with more than 26,000 homes included, the study provides one of the most comprehensive views yet.

By blending technology, climate data, and behavioral analysis, this research paints a fuller picture of how Americans use water indoors. The clearest lesson is simple: toilets and showers dominate.

But the surrounding story – about appliances, weather, and policy – shows that conservation requires more than one lever. It demands understanding the complex ways homes, habits, and environments interact.

The study is published in the journal Earth’s Future.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–