Shampooing twice adds 27% to your shower time: study

By Miles Harper

A University of Surrey study published in the Journal of Environmental Management finds that everyday hair‑care habits — not just low‑flow fixtures — are a major reason showers consume so much water. The researchers tracked thousands of showers and say routine behaviors such as repeated shampooing and intermittent rinsing significantly lengthen shower time, with direct consequences for household bills and local water demand.

The study and what it measured

Researchers combined smart bathroom sensors with post‑shower surveys to analyze 8,550 individual shower events across 319 households in Germany. Rather than relying on self‑reports alone, the team captured real usage patterns and then linked them to answers about what people were doing while the water ran.

Sensores inteligentes en un baño rastreando datos de ducha
Los sensores de baño inteligente capturaron patrones de uso real en 8.550 eventos de ducha.

Key behavioral drivers emerged clearly. Shower sessions that included shampooing more than once took substantially longer, and people who turned the water off while lathering tended to extend their overall time in the bathroom compared with those who kept the flow on.

Behavior Typical change in shower duration
Shampooing two or more times About 27% longer
Turning water off while lathering Roughly 20% longer
Age under 50 Tended to have longer showers than older adults
Soft water in the home Associated with longer showers (likely due to richer lather)

Why this matters today

Showers already account for an outsized share of indoor water use—typically between about a quarter and nearly half—so small changes in routines can add up to meaningful savings for households and utilities alike.

Grifo de ducha con agua corriendo, ilustrando el uso de agua doméstica
Reducir el tiempo de ducha ahorra agua y energía para calentar.

With water costs rising in many regions and utilities planning for hotter, drier summers, understanding which habits drive extra minutes (and gallons) in the shower gives immediate, practical leverage for conservation efforts. Cutting shower time also reduces the energy used to heat water, linking personal choices to both bills and carbon emissions.

What the findings mean for people and policymakers

The researchers note that installing a low‑flow showerhead is still helpful, but the single biggest lever is behavioral: shorten the time you spend washing hair and question rituals that repeat shampooing or extend rinsing. For utility planners and conservation programs, messages aimed at routine behaviors could be more effective than hardware incentives alone.

  • Focus on shower duration—every minute saved reduces both water and energy use.
  • Re-evaluate whether double‑shampooing is necessary for your hair type; the study links it to substantially longer showers.
  • Be cautious about “turning the water off” while lathering; that practice can increase total time in the shower if it leads to longer overall sessions.
  • Combine fixture upgrades (like low‑flow heads) with behavioral nudges for the best results.

Behavioral shifts are not a silver bullet, but they are immediate and low‑cost. As utilities and households wrestle with higher bills and the effects of climate variability, changing small bathroom habits may be one of the simplest ways to reduce water demand now.

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