Using a low-flow showerhead is a great way to lower your home’s water usage. Whether your reason for using this water-saving device is to help preserve natural resources for future generations, thus living a “green” lifestyle, or because you want to save money on your utilities is largely unimportant. At least in this context. Low-flow shower heads do help with water conservation, regardless of your motivation. However, if your goal in choosing a lower-gpm (gallons per minute) flowrate showerhead is strictly financial, meaning you want to spend less money on water, electric or gas bills, knowing exactly how much money you’re saving is pretty important.
I covered the water-savings aspect of low-flow showerheads before, but that only took into account the number of gallons saved over the course of a month or year. And, if you read through it, I took the conservative approach: a single person taking 25, 7-minute showers over the course of one month would use 2,000 fewer gallons of water annually by using a 1.5gpm low-flow shower head vs. the traditional low-flow 2.5gpm showerheads being sold today. That’s a fair amount of water saved, and it quickly adds up when you add more people to the household or account for longer showers. That said, water savings is only a small part of the overall big picture.
Because this turned out super-long with a lot of technical stuff (math) thrown in which you may or may not be interested in, here’s the layout of the “money saved with low-flow showerheads” findings:
- How we calculate money saved
- Calculating “normal” showerhead costs
- Gas water heater costs
- Electric water heater costs
- Per-shower, monthly and annual costs – 2.5gpm showerhead
- Calculating low-flow (1.5gpm) showerhead costs
- Money saved using a low-flow showerhead
- Summary: do low-flow showerheads really cost less?
Calculating money saved using low-flow showerheads
While the math for calculating the gallons of water saved using a low-flow showerhead is easy and straightforward, calculating how much money you save using a lower-flow-rate shower head is far from easy, simple or straightforward. There are many more variables at play beyond a showerhead’s gallons-per-minute dispersal rate and how many minutes a shower runs for over a period of time:
- Gas vs. electric water heater
- The efficiency of the water heater
- The size of the water heater (how many gallons it holds)
- The water temperature before heating
- The water temperature after heating
- The cost of electricity or gas
- And finally, the water and sewer rates for the individual or household
I’ve been wanting to put this post together for months, but the daunting task of trying to get averages, statistics and specs for all of the above variables proved exceptionally time consuming and prohibitively difficult.
Recently, however, when looking for showerheads to add to the shower head comparison list, I stumbled on a footnote on related site that helped immensely, so much so that it allowed me to move forward with this project.
So, to calculate how much money is saved by using a low-flow showerhead, I’m going to use the following statistics and metrics:
- Average water heater size: 40 gallons [source]
- Average water heater efficiency [source 1,2,3,4]
- Gas water heater: 59%
- Electric water heater: 92%
- Average cost of electricity (USA): $0.12 per kilowatt hour (kWh) [ source ]
- Average cost of water and sewer per 1,000 gallons (USA): $5.34 [source]
- Average cost of gas per 1,000 cubic feet(USA): $16 [source]
We’re also going to use some assumptions regarding water temperatures that look to be average:
In all, my goal here is to give you a relative gauge regarding just how much money you may potentially save using a low-flow showerhead, just not an exact figure.
Monthly and Annual Costs of using a “regular” showerhead (non low-flow)
Before we can get into how much money is potentially saved using a low-flow showerhead, we need to calculate how much money a standard showerhead, which we consider 2.5gpm, costs to use over a period of time. For continuity’s sake, we’ll stick with the scenario laid out in our water savings statistics post:
- 1 person taking 25, 7-minute showers over the course of a one-month period with a standard, 2.5 gallons per minute flow-rate shower head.
In this example, there are about 437 gallons of water used in a one-month period for showering purposes only. However, on a per-shower basis, that’s 17.5 gallons of water per shower. So…
In a 40-gallon water heater with a starting temp of 120°F, you use 17.5 gallons of water and leave approximately 22.5 gallons in the tank after a single shower. The incoming water is 55°F, and the resulting mixed temperature of the water in the water heater is around 91°F* So, we need to raise 40 gallons of water from 91°F to 120°F or 29°F.
*Here’s how I got the 91°F figure: One gallon of water weighs about 8.34 pounds. That’s 133.44 ounces. Converting the gallons of water used (17.5, “cwOZ” or cold water) and the number of gallons remaining in the tank (22.5, “hwOZ” or hot water) to ounces, you get 2335 and 3002, respectively. “cwT” and “hwT” refers to cold water (17.5 gallons @ 55°F) replacing water used for the shower and hot water (22.5 gallons @ 120°F) in the tank. Here’s the formula:
((cwOZ*cwT)+(hwOZ*hwT)) / (cwOZ+hwOZ) = Mixed Water Temperature (91.567…)
To calculate how much energy is used (BTUs) to raise the temperature of one gallon of water, we take the weight of a gallon of water (8.34 pounds) and multiply that by the difference between the current water temperature and the target water temperature:
8.34 * 29 = 241.86 BTUs
Before we break down the heating costs involved gallon or shower, here are some conversions we’ll be using:
- 1 CF (“cubic foot”, gas water heaters) is approximately 1,020 BTUs
- 1KWh (“kilowatt hour”, electric water heaters) is approximately 3,412 BTUs
Also, this source was the basis for this section.
Gas water heaters: costs to heat water
At 100% efficiency, it’d take a gas water heater 241.86 BTUs to bring one gallon of water back up to temp after a 7-minute shower. Let’s call it 242 BTUs. However, since gas water heaters aren’t 100% efficient, we need to calculate the more-likely number of BTUs used to heat the water. We do that like this:
Number of BTUs used / Efficiency% = Actual BTUs used, or 242 / 59% = 410 BTUs
Then, to calculate how many BTUs are used to re-heat the water heater after the shower, we multiply the number of BTUs (410) by 40 gallons (water heater capacity) which results in a total of 16,400 BTUs.
Since there are 1,020 BTUs in a cubic foot of gas, a single shower uses 16.08 cubic feet of gas, which when billed at $16 per 1,000 cubic feet ($0.016 per cubic foot) results in a heating cost of $0.26 per shower, or about $0.015 per gallon.
Electric water heaters: costs to heat water
Since electric water heaters are around 92% efficient, we’ll just plug that into the formula used to calculate the heating costs for gas water heaters:
Number of BTUs used / Efficiency% = Actual BTUs used, or 242 / 92% = 263 BTUs
Since there are 3,412 BTUs in 1 kilowatt hour (which averages about $0.12 per), heating a single gallon would use .077 kWhs, thus resulting in a water heating cost of $0.37 per shower or $0.02 per gallon. (.077kWh per gallon heated * 40 gallons = 3.08kWh)
Factoring in the costs of water and sewer fees
With water and sewer rates combined running at $5.34 per 1,000 gallons (or $0.00534 per gallon), the 7-minute, 17.5 gallon shower costs roughly $0.09 per shower ($0.09345).
So, overall, the average costs of 25, 7-minute showers per month using a 2.5gpm showerhead cost as follows:
Gas water heater
- Cost per shower: $0.35
- Cost per month: $8.75
- Cost per year: $105
Electric water heater
- Cost per shower: $0.46
- Cost per month: $11.50
- Cost per year: $138
Monthly and annual costs of using a low-flow showerhead
Using our flowing example, we’ll switch out the 2.5gpm showerhead for an eco-friendly 1.5gpm shower head. So, instead of each 7-minute shower using up 17.5 gallons of water, we’re only using 10.5 gallons.
- Our “mixed” water in the water heater starts at 103°F and only needs to be raised 17°F after the shower
- We use 141.78 BTUs to reheat the water in the water heater at 100% efficiency, but really use 241 BTUs for gas water heaters and 154 BTUs for electric water heaters with the lower-gpm shower head
- Total energy usage for bringing the water in the water heater back up to temp is 9.45cf for gas, 1.8kWh for electric heaters
- Because we’re using less water, our per-shower water and sewer costs go down to $0.06 per shower vs $0.09 per shower
So, when we crunch the numbers, we come up with this:
Shower costs using a 1.5gpm showerhead
Gas water heater
- Cost per shower: $0.21
- Cost per month: $5.25
- Cost per year: $63
Electric water heater
- Cost per shower: $0.28
- Cost per month: $7
- Cost per year: $84
Money saved using a low-flow shower head
Percentage-wise, replacing a standard 2.5gpm showerhead with a 1.5gpm low-flow shower head saves you around 40% annually (actually, every time). In terms of real-dollars saved per-shower, monthly and annually:
Gas water heater – 40% savings
- Savings per shower: $0.14
- Savings per month: $3.50
- Savings per year: $42
Electric water heater – 39% savings
- Savings per shower: $0.18
- Savings per month: $4.50
- Savings per year: $54
Does a low-flow showerhead really save you money?
In a large majority of cases, absolutely. You can find Eco-friendly showerheads for as little as $5, but as high as $100 or potentially more depending on your needs and tastes. Lowering your shower’s gallons-per-minute dispersal rate by one gallon, which can still offer strong shower pressure, can offset the costs of the lower-water-usage showerhead within a couple of months or even weeks depending on your energy costs, water costs and showering needs.
So, regardless of whether you want to help preserve today’s natural resources for tomorrows generations or you want to lower your water and energy bills, replacing your existing showerhead with a lower-flow model can help you do a bit of both.
Feel free to check out our showerhead comparison guide – it lists a large number of low-flow showerheads that you can sort by price, rating and flow rate. Or, you could always head over to eBay or Amazon to find the best deals on showerheads today.
I hope you’ve found this guide helpful, but if you have any questions, feel free to leave a comment below.