Hydraulics of getting the freshest water

Discussion in 'Architecture & Engineering' started by TheVat, Oct 20, 2023.

  1. TheVat Registered Member

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    With all the current fuss about plastic, the Vat household was pondering our PEX piping and its potential for adding leached chems or plastic nanoparticles to our tapwater. The popular wisdom seems to be let the water run a minute, especially on arising. Now my field is biology (plus some brushes with information sci), so my understanding of hydraulics is limited to a few bits of brain flotsam regarding the vascular system, i.e. extremely limited.

    What I wonder is how exactly pipes drain. If I just run one tap, does a cylinder of moving water go directly from the main hookup in the basement to that tap, leaving other water lines fairly "stagnant" or does the whole network contribute to some degree? IOW, would it more efficiently freshen our water lines to go about and run all the taps in the morning, or is it okay to just run one tap longer? My intuition is that running all taps a little might be better, albeit time-consuming, and more efficiently flush out any leachate etc.

    And yes, I've considered copper plumbing, though both expense and lower tolerance of freezing are not pluses here, where lows of minus 20 F. are not uncommon. PEX is popular here especially where piping must go through poorly heated spaces.

    (and a shoutout to any members of scienceforums dot net who may wander through - that venerable site has fallen into a coma this week, from which it hopefully will emerge when Blike remembers to renew the domain name)
     
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  3. exchemist Valued Senior Member

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    Yeah I wondered what had happened to the .net site.

    I can’t claim to be an expert but I would have thought running only one tap will only flush the path to that tap. The rest will stay largely stagnant, I imagine. But in most homes it is the tap in the kitchen that is used for >90% of drinking water so I think I would be relaxed about the others. I doubt there is a risk from microplastics due to plastic piping, once it has been flushed after being fitted.

    Regarding the pipes to other parts of the house, flushing toilets and running showers should turn the water over in most of the system.
     
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  5. DaveC426913 Valued Senior Member

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    ^ Wut he sed.

    But, like, gooder words n stuf.
     
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  7. exchemist Valued Senior Member

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    Great Clueless Husband impression

    Please Register or Log in to view the hidden image!

    .
     
  8. TheVat Registered Member

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    Given you're using upper case, I gather that's a member name and not a general allusion to clueless husbands. Which would be a verry general allusion!

    Thanks for your take on the plumbing situation. In a pressurized system, a fairly direct flow from main to tap does sound correct. My only remaining question is on high density polyethylene (the stuf PEX is made of) and if there is longer-term leaching from the pipe interior that would be of any significance. It's probable that the current plastic paranoia is overblown, but I'll look a little more at the research. Happy news, so far: it doesn't contain BPA and factory residues flush out quickly.
     
  9. exchemist Valued Senior Member

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    I feel sure that running the kitchen tap for a couple of minutes first thing in the morning should be adequate.

    Don't forget that if you flush a toilet upstairs or take a shower, before coming down to get water for drinking, that will clear out the line as far as that point, so it would only be the remaining spur into the kitchen itself that might conceivably benefit from flushing.

    We had a think about this actually when our son was born, because the main into the house from the street is lead! It probably dates from Victorian times when the houses in our street were built. (We got the Pb level tested and it was well within safety limits, in part because the water in London is hard and lays down a layer on the surface of the pipe, covering the lead.) In our house the toilets and showers are fed from a header tank in the roof, so whenever one of these is used, the water in the header tank is replenished from the main. The riser branches off in the cellar. So it is only the run of pipe from where the riser branches off into the kitchen that is not already flushed by the time we come downstairs in the morning - and that bit is all copper.
     

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