The moment you’re putting a bath bomb in the tub and trying to unwind at the end of a long day is the worst time for your flow rate to drop. But if you’re in a household of more than four people, or your dishwasher is running while you’re about to bathe, then experiencing pressure drop isn’t just a hypothetical, it’s a sure thing.
When we talk about water, we often talk about its flow; how it flows in rivers, streams, large bodies of water. But there’s also a technical definition of water flow — the water flow rate and how it affects your ability to use it comfortably in your own home. Unfortunately, in an industry lathered with plumber’s jargon, there’s a lot of confusion around what your water flow rate is, and if installing a water filter will make your pressure drop.
Water Flow Rate vs Water Pressure
First, let’s understand the difference between your water flow rate and your water pressure. They might sound like similar terms, and they both have to do with friction, but they differ enormously.
Your flow rate refers to the amount of water coming out of your faucet in a certain amount of time. We break down the math of measuring your water flow rate below.
Water pressure, on the other hand, is determined by gravity rather than speed. Your home water pressure is the force exerted upon the water to get it from point A to point B.
Flow Rates by Household Size
Your water flow rate, also known as your Gallons-per-Minute or GPM, is the measurement of how many gallons of water could potentially come out of your kitchen faucet or bathtub per minute.
Your flow rate depends on a mix of factors, but the first thing is your household size. Standard household sizes are 2-4 people. After four people, you’re considered a “large household”. That small difference in verbiage makes all the difference when you’re trying and failing to rinse out your coffee mug in the morning.
But the classification of “large household” doesn’t automatically mean that your flow rate is destined to be lower than others; the thing that hampers your flow rate is the likelihood that many people will be using water within the same house at the same time.
Flow Rates by Square Footage
The second factor that affects your water flow rate is the square footage of your home. Determining your flow rate per square foot can actually be broken down using a simple equation. In layman’s terms, this equation determines what your water filter loading capacity will be, your media backwash rate, and will also help you understand if and when you’ll experience pressure drop.
The typical inlet water pressure to a standard size home is usually between 40 to 45 pressure-per-square-inch (psi). For a standard household, it should never exceed 60 psi— that’s why many plumbers automatically set your pressure regulator to 50 psi. But it’s important to remember that no matter how you configure your psi, not all homes are standard. That’s why pressure regulators can be changed between 25 and 75 psi without even breaking a sweat.
So, if the standard home square footage in the United States is 2,322 sq. ft., then it’s reasonable to assume that any home that is above that could potentially experience a diminishing flow rate.
How to Calculate Your Water Flow Rate
Luckily, your flow rate per faucet is easy to calculate. Start by turning your faucet on full blast and fill a measuring cup or container for 10 seconds. If you’re measuring in cups (U.S.), convert that number from cups to gallons. Then, according to The Spruce, all you need to do is “multiply the measured quantity of water by 6 to calculate the flow rate in gallons per minute.” It’s that easy.
Compare that with standard flow rates across the U.S. For the standard home, a typical GPM looks something like this:
- Kitchen faucet: 2-3 GPM
- Shower: 1.5-3 GPM
- Dishwasher: 2-4 GPM
- Washing machine: 3-5 GPM
If those average flow rates are correct, running all those faucets at the same time would result in a pressure drop.
Laws Designed to Protect Your Flow Rate
Luckily, there are laws in place to make sure your appliances don’t exceed a reasonable GPM.
Since 1992, a maximum of 2.5 GPM is the EPA-mandated flow rate for new showerheads. This means that no more than 2.5 gallons of water should be flowing out of your shower head at any given minute.
…no more than 2.5 gallons of water should be flowing out of your shower head at any given minute.
Additionally, manufacturers have decreased the flow rate for showerheads over time. If your current shower head was made in the 1980s or 1990s, your flow rate could be 3.5 GPM or more.
How Does Flow Rate Affect Water Filtration
If the incoming water pressure is too high, you’ll need a flow restrictor installed on your water filter to slow water down before it passes through your water filter.
When you start your researching process, look for a water filter that can handle at least 5 GPM, and then consider your water quality, contaminants you’re looking to eliminate, and your budget. Do you want to filter from just your kitchen faucet? Or do you want to filter across your whole home?
Do you want to filter out chlorine/chloramines, or do you also want to tackle fluoride and mercury? Do you want your bath to be free from contaminants or just your kitchen faucet?
Look for the IAPMO or NSF Certification
At the end of the day, the best way to know that you’ll experience filtered water at proper flow rates is by looking for the IAPMO or NSF seal and comparing the system performance results with your own average household flow rates.
…the best way to know that you’ll experience filtered water at proper flow rates is by looking for the IAPMO or NSF seal…
IAPMO is an independent nonprofit testing organization that certifies to NSF International standards. If a filtration or softening system is IAPMO certified to NSF/ANSI Standard 44, for example, this means that the performance of the system is confirmed to testing standards in a lab. Certifications have to meet an efficiency rate of 85 percent or greater in order to pass and receive certification status and they are a surefire way to make sure that the product you’re investing in will help give you access to clean, healthy water, regardless of environmental factors or household size.
Many whole house filtration systems have been NSF/ANSI tested and certified to make sure that peak times or not, your household will have access to filtered water. For example, our Rhino 600,000 Gallons Whole House Filter is tested and certified to reduce contaminants up to 7 gallons per minute. Same with the Rhino 1,000,000 Gallons Whole House Filter – certified for contaminant reduction up to a flow rate of 7 GPM. Because at the end of the day, getting access to clean, filtered water shouldn’t mean you have to sacrifice a warm bath.