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A 20-minute shower can use a lot of water. Whether it is truly a waste depends on the showerhead, how often you take long showers, and how limited your water supply is.
A standard showerhead can use about 2.5 gallons per minute (gpm). At that flow rate, a 20-minute shower uses about 50 gallons. A WaterSense-labeled showerhead uses no more than 2.0 gpm, which would use up to about 40 gallons in 20 minutes.
If you depend on stored rainwater, a well, or another limited supply, that difference can become important very quickly.
How Much Water Does a 20-Minute Shower Use?
You can estimate shower water use with a simple formula:
Shower time × showerhead flow rate = gallons used
Here are some examples:
| Showerhead flow | 5-minute shower | 10-minute shower | 20-minute shower |
|---|---|---|---|
| 1.5 gpm | 7.5 gallons | 15 gallons | 30 gallons |
| 2.0 gpm | 10 gallons | 20 gallons | 40 gallons |
| 2.5 gpm | 12.5 gallons | 25 gallons | 50 gallons |
The actual amount can be lower if you turn the water off while washing or if your showerhead flows below its rated amount.
It can also be higher with older fixtures or showers that run several heads or body sprays at once.
Is 20 Minutes Too Long for a Shower?
From a water-use point of view, 20 minutes is a long shower.
Cutting a 20-minute shower to 10 minutes roughly cuts its shower water use in half, assuming the same flow rate.
For example:
- 20 minutes at 2.0 gpm = about 40 gallons
- 10 minutes at 2.0 gpm = about 20 gallons
- 5 minutes at 2.0 gpm = about 10 gallons
That does not mean every 20-minute shower is unreasonable. Someone may occasionally need more time. The larger issue is making long showers a daily habit.
A person taking a 20-minute, 2.0-gpm shower every day would send about 40 gallons through the shower each day. Shortening it by 10 minutes would reduce that by about 20 gallons per shower.
EPA says showering accounts for nearly 17% of residential indoor water use in the average U.S. home.
Your Showerhead Matters Almost as Much as Your Shower Time
Two people can shower for the same amount of time and use very different amounts of water.
A showerhead's flow rate tells you how much water passes through it each minute. It is normally listed in gallons per minute, or gpm.
A 20-minute shower with a 1.5-gpm showerhead uses about 30 gallons.
The same 20 minutes at 2.5 gpm uses about 50 gallons.
That is a 20-gallon difference without changing the shower time.
In the United States, EPA notes that standard showerheads use 2.5 gpm, while WaterSense-labeled showerheads must have a maximum flow rate of 2.0 gpm. WaterSense models must also meet performance requirements for factors such as spray force and coverage.
How to Find Your Shower's Actual Water Use
Do not assume your showerhead uses exactly what is printed on the label.
Water pressure, deposits, fixture design, and other conditions can affect actual flow.
You can make a simple measurement with a bucket and timer.
- Place a bucket under the shower.
- Run the shower at your normal setting.
- Collect water for a known amount of time, such as 30 seconds.
- Measure how much water you collected.
- Convert that amount to gallons per minute.
For example, if the shower produces 1 gallon in 30 seconds, its approximate flow is:
1 gallon × 2 = 2 gpm
At that rate, a 20-minute shower would use about 40 gallons.
This measurement is often more useful than guessing from the age or appearance of the showerhead.
Why Long Showers Matter More With Stored Rainwater
Shower length becomes especially important when your home or cabin depends partly on stored water.
Suppose you have a 500-gallon storage tank. A 20-minute shower using 2.0 gpm consumes about 40 gallons.
That is about 8% of the tank's nominal capacity from one shower.
Ten similar showers would use about 400 gallons before considering:
- toilet flushing
- sinks
- washing
- irrigation
- leaks
- pump requirements
- unusable water near the bottom of the tank
A tank's stated capacity is also not always the same as the amount of water available to your plumbing system.
If several people use the system, shower demand can quickly become one of the largest regular draws on storage.
Do Not Size a Rainwater System Around Tank Capacity Alone
A large tank does not mean you can use large amounts of water indefinitely.
Rainwater supply depends on how much water your roof can collect and how often rain arrives.
A system that stores 1,000 gallons but receives little rainfall during part of the year can still run short.
When planning shower use, consider the whole water balance:
water collected − water used − system losses = change in stored water
Shower demand should be counted along with every other regular use.
For example, reducing one person's shower demand from 40 gallons to 20 gallons per day could make a meaningful difference in a small cabin or off-grid system.
The same reduction may matter much less to a home connected to a reliable public water supply.
Can You Use Rainwater for Showers?
Consider the number of showers available from 1,000 gallons to evaluate this decision within the complete collection path.
Using collected rainwater for bathing requires more care than using it for garden irrigation.
Roof runoff can collect bird droppings, insects, dust, roofing debris, microorganisms, and other contaminants. Water quality can also change while it sits in storage.
Do not assume that clear-looking rainwater is safe for showering.
A household rainwater system may need several stages, such as debris control, suitable storage, filtration, disinfection, and ongoing maintenance. The correct setup depends on the collection surface, local requirements, intended use, and water quality.
A first-flush system is one example of pretreatment. It diverts some of the first runoff from a roof instead of sending that dirtier initial water directly into storage. It can reduce contamination entering the tank, but it does not by itself make stored rainwater safe for household use.
If rainwater will be used where people may inhale mist, get water in their eyes or mouth, or have prolonged skin contact, treat water quality as a whole-system issue. Follow current local health and plumbing requirements and use qualified help when needed.
Ways to Reduce Shower Water Use Without Rushing
You do not have to turn every shower into a race.
A few simple changes can reduce water use significantly.
Shorten the running time
Reducing a shower from 20 minutes to 15 minutes cuts running time by 25%.
At 2.0 gpm, that saves about 10 gallons.
Dropping from 20 minutes to 10 minutes saves about 20 gallons.
Use a lower-flow showerhead
A lower flow rate reduces water use every minute the shower is running.
Changing from 2.5 gpm to 2.0 gpm reduces flow by 20%.
EPA's WaterSense program uses 2.0 gpm as the maximum flow rate for labeled showerheads.
Turn the water off when you do not need it
If your plumbing makes it practical, shutting off the spray while shaving or doing another task can reduce actual running time without shortening the whole bathroom routine.
Fix leaks and dripping controls
Water use does not stop being important when the shower ends.
A valve or showerhead that continues dripping can add unnecessary use over time. Repair persistent plumbing leaks rather than treating them as normal.
A Practical Target for Rainwater Users
There is no single shower length that works for every household.
For a home with limited stored water, it is more useful to set a water budget than an arbitrary time limit.
Start by finding your shower's flow rate.
Then calculate:
gpm × minutes × number of showers = shower demand
For example, two people each taking a 10-minute shower at 2.0 gpm would use about:
2 × 10 × 2 = 40 gallons per day
If both take 20-minute showers instead:
2 × 20 × 2 = 80 gallons per day
That extra 40 gallons must come from somewhere.
In a rainwater system, it means you need enough collection, storage, and dependable rainfall to replace it. If the numbers do not work, reducing shower time is often easier than adding another large storage tank.
Frequently Asked Questions
How many gallons does a 20-minute shower use?
It depends on the showerhead's flow rate. At 1.5 gpm, a 20-minute shower uses about 30 gallons. At 2.0 gpm, it uses about 40 gallons. At 2.5 gpm, it uses about 50 gallons.
Is a 10-minute shower better than a 20-minute shower?
Yes, if reducing water use is the goal. With the same showerhead and flow rate, cutting the shower time from 20 minutes to 10 minutes roughly cuts the water used in half.
How much water does a 5-minute shower use?
A 5-minute shower uses about 7.5 gallons at 1.5 gpm, 10 gallons at 2.0 gpm, or 12.5 gallons at 2.5 gpm.
How can I tell how much water my showerhead uses?
Check the showerhead for a rated flow in gallons per minute, or measure the actual flow with a bucket and timer. Measuring can give you a better estimate of what your shower is using under your home's water pressure.
Does a low-flow showerhead really save water?
Yes. A lower flow rate means less water passes through the showerhead each minute. For example, a 2.0-gpm showerhead uses about 20% less water per minute than a 2.5-gpm showerhead.
Is a 20-minute shower a problem with a rainwater tank?
It can be. A 20-minute shower at 2.0 gpm uses about 40 gallons. That amount can take a noticeable share of a small rainwater supply, especially when several people shower every day.
Can untreated rainwater be used for showering?
Do not assume untreated roof runoff is suitable for showering. Roof runoff can contain biological and chemical contaminants. Household use requires appropriate collection, treatment, maintenance, and compliance with applicable local health and plumbing requirements.
