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Reasons to avoid low-flow shower heads and pick the best water-saving shower head instead

Updated: Sep 18



As a significant part of the country is experiencing drought conditions, many of us are probably considering switching to a water-saving shower head or a low-flow shower head to combat the increasing water and energy price and also help the environment. Interestingly, when you look for a solution to this the internet and government or even local water districts recommend low-flow shower heads as a basic solution. However, the devils are in the details.


Those who have tried them know that it is a compromised solution, no more strong, heavy rainfall or waterfall sensation, no more immersive water coverage like the big shower heads, and quite surprisingly, it might not actually save that much water.


Yes, you read that correctly. Standard low-flow showers tend to not save as much water and energy as promised. Let’s take a deep dive into low-flow shower heads, and learn why we created a better alternative, the Oasense Reva smart sensor shower head, to help you preserve the best part of the shower experience while saving more water effortlessly.


What is a low-flow shower head?


A low-flow shower head is commonly regarded as a shower head that has flow rates lower than 1.5 gpm. The standard way to measure shower head flow rate is to measure at 80 psi in coming pressure so we can compare between different brands and models.


How to choose a low-flow shower head:


Well, if you ask us, the answer is easy. Don't even think about it. Pick the Oasense Reva instead, here’s why:


So what are the common myths about low-flow shower heads?


We will address some of the common beliefs here in detail and why they are not true.

  1. low-flow shower heads work as intended to save water

  2. low-flow shower heads provide a good shower experience

Let's look into it:


A. How much water does a low-flow shower head save?


Answer: Not as much as commonly believed.


Almost every low-flow shower head claims to save water, but is it really that simple? You probably have seen a demo like this:


  • Two fish tanks and a timer

  • One shower head with 2.5 gpm flow rate, another one with 1.2 gpm flow rate.

  • Point both shower heads to a fish tank respectively, start the water and the timer, timed for 5 mins.

  • Surprise surprise! The 1.2 gpm shower head only fills up half of the fish tank whereas the 2.5 gpm shower head fills it up!

  • You just saved 50% of the water! Congratulations!


This type of tautological demonstration is everywhere, you see them on YouTube, on blog posts, and in commercials. But does that hold true? In fact, this is a misleading simulation of the real situation and not quite the journey you will have while using one.


Of course, when you use a fixed timer and time different GPM ratings, you will get different amounts of water coming out. That is the definition of “gallon per mins”, however, does gallon per min translate directly to water saving? If I use a 0.1 GPM shower head for the shower, do I save 96% of my shower water? See the caveat of this? It is not possible to just cut the water in half and claim all water saved because when the water flow is restricted, showers time changed and often become longer. You probably need to shower 100x longer with a 0.1 GPM shower head to get the same cleanliness compared to a 2.5 GPM shower head if the 0.1 GPM flow rate is really shower-able. This is just one of the reasons why we think that low flow is not the answer to our water problem, as a reduction in flow only encourages longer showering times in order to achieve the desired rinsing amount.


Why low flow (low GPM) does not mean lower water usage and energy saving?


There are two main factors for this, one being, facilities and secondly, human behavior.


1. Warm-up efficiency is bad for low-flow shower heads.

Those who have made the switch from a higher flow to a low-flow shower head may know what the problem is here. You installed a new lower flow shower head and waited 5 or even 10 more minutes just to purge out the cold water. Well, it is definitely not your plumbing, it’s the shower head. This is sadly a reality for low-flow showers as they take longer to pull the hot water from your tank and it consumes more energy and water than you think.


In plumbing systems, when we restrict the output flow rate, we not only elongated the time where hot water travels through cold pipes to reach the shower head, but we also introduced more chances of turbulent flow in the pipe where more cold water is mixed with hot water instead of being pushed out by that latter. This results in a lower overall temperature, more heat loss to the ambient temperature due to the prolonged amount of time that the water has stayed in the pipe, which leads to a much longer warm-up time.


We can not quote enough of the detailed study done by Evolve which makes thermal shut-off valves for hot water reservations. The effect of limiting the flow rate to a longer warm-up time is not linear, but exponential. We are waiting more than six times longer for hot water compared to the pre-1992 era. And if we further limit the flow rate to the low-flow regime, then the wait time would be a lot worse. The study has also shown that warm-up water waste consists of up to 30% of the water shower waste on average, that’s the data with all flow rates blended together. If we look at low flow only, the warm-up waste would be a lot worse. And keep in mind, that shower water is “hot water”, and water has great heat capacity. Wasting heated water is wasting both energy and water.


To counter this problem, we recommend that you either don’t use a low flow shower head, and use TSVs like evolve or automatic TSV’s like the one embedded in the Oasense Reva, and maybe add the recirculation pump so you have instant hot water. Yet the recirculation pump uses a lot of electricity so the net might not be a worthwhile investment.


2. Rinse efficiency is bad for low-flow shower heads which means you have to rinse for longer