There are, or should be some guiding lights to follow when designing and building good plumbing systems. The basic concepts are simple.
The first point sounds simple, but did you know that over 70% of the hot water draws in most homes do not deliver hot water? Who is willing to wait for hot water when rinsing hands? Most of us aren’t, but we turn on the hot tap anyway and finish before the hot water arrives.
And, have you ever heard of or done the “shower dance”? That’s when you are showering and somebody flushes a toilet, unbalancing the system and giving you a jolt of hotter or colder water than you were using, causing you to do the limbo away from the shower water. Extrapolating from this article: https://blog.aarp.org/healthy-living/beware-the-most-dangerous-room-in-the-house there are about 188,000 injuries in the US requiring an emergency room visit each year from falls in the bathroom, many around bathing. If you have to do the shower dance, now is the time to install a pressure balancing shower valve! So in addition to being inconvenient and unpleasant, unsteady temperatures can lead to life threatening falls. That’s rather unhealthy and it leads us to the second point about safety.
Uneven temperatures can lead to falls, but also scalding. Old and very young people may not be able to sense or communicate it when they are getting burned. Another thing that plumbing can give us is bad bugs, like legionella or ultimately Legionnaire’s disease. The balance between scalding and bad bugs is something the plumbing community has been struggling with for decades. Temperatures over 130 F effectively deal with most bad bugs, but that temperature also can burn people in not very many seconds. This problem can be helped with anti-scald shower valves and mixing valves, but ultimately, education of the populace in general is probably the best defense, so people don’t unknowingly put themselves in harm’s way. This leads me to the next topic, being energy and water efficient.
Probably the first thing to keep on top of mind when looking for efficient plumbing systems is to keep the volume of water between heater and end use as small as possible. Why? Well, if there isn’t a lot of cooled water in the hot line, you don’t need to run as much water or wait as long for hot water to arrive. Also, you haven’t spent so much money to heat water that simply cooled off in the pipes. One can reduce volume by having shorter or skinnier pipes, … or both! Shorter pipes means putting all the wet rooms close together and keeping the water heater close by as well. That’s best done in new construction or when a gut remodel is being done. Skinnier pipes can happen when it’s time to re-pipe or just because you’re tired of waiting for hot water. A rule of thumb is that for every size up in piping materials, you roughly double the volume of water in the line. So, if you go from ½” to 3/8” pipe, you’ve cut the volume in half. That means you’ll wait half as long to get hot water :~) This also means you will have needed to heat only half as much water for the plumbing. So, there is a 50% savings in the plumbing without even mentioning insulation. But now that I’ve used the “I” word, let’s think about what that can do for you. Here is an article written by my friend Gary Klein: http://www.garykleinassociates.com/PDFs/15%20-%20Efficient%20Hot-Water%20Piping-JLC.pdf He goes into some detail on insulation and the benefits of having it. The main point to me is that good insulation will slow cool down of the piping (and water in it), so after the first draw of hot water you will get much more time where the water in the lines remains at a usable temperature, essentially giving you hot water immediately on subsequent draws. This also saves water, which actually matters in some places…
It seems most plumbers don’t carry a pressure gauge, but they should! If you know what the static water pressure is, you can size the piping appropriately to the use. Now, should you install a really low flow showerhead and you know what the water pressure is, you’ll know just how small the piping or tubing to the shower valve can be. I would not be surprised to find lots of places where ¼” tube would be sufficient to supply a shower with good pressure if you had a not-too-long run of tubing. One health benefit of smaller tubing is that water flow in it speeds up and this scrubs off bio-films that can harbor those bad bugs we don’t want. There are lots of benefits from using right-sized plumbing including lower cost to buy and install. How does that relate to my next topic, being simple and durable?
Every piping material is good for a certain flow rate through it before any damage happens to the pipe. With copper it’s about four feet per second and with cross-linked polyethylene or PEX, it’s more like ten feet per second. With copper if you exceed that rate, erosion corrosion begins to happen.It’s like running sand through the line. The pipe gets worn down internally, getting thinner over time. Eventually you start to get pinhole leaks. PEX, which is particularly smooth on the inside, gives you two and a half times that flow rate before damage starts. So, if there is adequate pressure, using small diameter PEX tubing can give you good flow without affecting the life of the tube. Also, it’s much easier to run than rigid pipe as it can be snaked through walls much like wiring. Another thing about using resilient PEX is that it helps with the problems of water hammer and also freezing. It can expand slightly when necessary to take up some of the shock of water hammer or enough to allow ice to form. When the hammer or freezing is done, PEX returns to its original size with no damage. PEX is still not freeze proof, but is much more tolerant of freezing than copper. Good design can help by keeping the piping away from areas more subject to freezing. That sounds pretty durable to me! Good design will also keep the system simple so there are fewer moving parts to get stuck or fail.
The four categories listed above each influence the other. When thinking about good plumbing it helps to take your time and make sure you have enough information to be able to meet all four goals. Then you can think about other important things, like cats!
Looking back over my working life of 50+ years, it seems clear that self sufficiency has always been the best way for me to be useful. Now, mix in a strong interest in water in its many forms and the wide world of animals and you'll know what's important to me.