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“The flushing helped significantly in almost every case. Among water heaters where water levels first tested above 50 ppb, flushing dropped the lead levels on a

“The flushing helped significantly in almost every case. Among water heaters where water levels first tested above 50 ppb, flushing dropped the lead levels on average from 456 ppb to 20 ppb” They took samples from the tank as I understand before and after flushing. If it’s in the sample some of it presumably goes to the water you use.

mattmaroon 3y ago
Right so the hot water tank was trapping lead that, in your cold supply, just passed right through to your faucet. All that extra lead in the tank didn’t go to a faucet. Seems better.
- mlyle 3y ago
  Of course, it's complicated because the pre-dissolved lead and lead that's formed into salts, etc, is more bioavailable and less likely to pass through you. Presumably the water heater reaches equilibrium and doesn't remove lead forever-- you get equal rates of lead in and lead out. But the water heater may be making the lead more bioavailable.
  - mattmaroon 3y ago
    Perhaps. Or perhaps hot water picks up more leas from copper pipe solder out whatever downstream. That’s why this is a really dumb testing method considering a good one (just testing at the faucet) would have been as easy to do.
    - mlyle 3y ago
      Testing at the faucet is definitely going to end up identical in concentration (plus whatever it picks up in pipes in the house), but not necessarily bioavailability.
      - mattmaroon 3y ago
        I can’t find anything indicating there’s any difference in bioavailability between hot and cold water, or that it’s a concern at all. I’d just assume whichever has less lead in it is what I’d rather drink. If the hot water tank is removing lead from the supply and trapping it, I think I’d rather use it for cooking. (Of course I’m not trying to drink warm water out of the tap in any case. ) And in any case what this study is measuring seems to have little relation to what you actually want you know. But I’d guess you’re right, the hot water tank is probably removing some lead (hence the higher concentration) but not enough to matter much. I strongly suspect the people who say you shouldn’t drink hot water are just parroting something that may be entirely mumbo jumbo, or may be true in some instances for homes with older plumbing but not anymore. I’ve replaced all the plumbing between the street and my kitchen with Pex so there’s no solder after the water heater. (Perhaps hot water does dissolve more lead from that, though I still have a hard time believing it is significant.)
        mlyle 3y ago
        > I can’t find anything indicating there’s any difference in bioavailability between hot and cold water, or that it’s a concern at all. Bioavailability of lead salts (like that form when you have a lot of hot water, metallic lead, and other contaminants in a tank for a long time) is higher than of metallic lead. Similarly, bioavailability of dissolved lead is higher than that of metallic lead particulate. The mechanism we're discussing is metallic lead particulate sitting in water heaters and dissolving. > I strongly suspect the people who say you shouldn’t drink hot water are just parroting something that may be entirely mumbo jumbo, or may be true in some instances for homes with older plumbing but not anymore. I suspect the people who say you shouldn't drink hot water have looked at the grody water that comes out when you drain a heater that's sat for a long time and see all the sediment and yuckies that accumulate at the bottom.
        mattmaroon 3y ago
        I suspect so too and again, their thinking is obviously incorrect. Those sediments and yuckies were all taken out of the hot water supply, but passed right through to the faucet on the cold side. Every time I drain my water heater, I dumped a bunch of sediment and yuckies down the drain that otherwise would have been in me, if I were drinking from the hot side rather than the cold. The logic you’re describing is like looking at a gross filter you’re replacing and saying “look at all this junk in the filter, I’m never filtering my drinking water again!” Filters look gross when you replace them for the exact same reason that hot water tank is full of sediment. It removed them.

mattmaroon 3y ago

Right so the hot water tank was trapping lead that, in your cold supply, just passed right through to your faucet. All that extra lead in the tank didn’t go to a faucet. Seems better.

mlyle 3y ago
Of course, it's complicated because the pre-dissolved lead and lead that's formed into salts, etc, is more bioavailable and less likely to pass through you. Presumably the water heater reaches equilibrium and doesn't remove lead forever-- you get equal rates of lead in and lead out. But the water heater may be making the lead more bioavailable.
- mattmaroon 3y ago
  Perhaps. Or perhaps hot water picks up more leas from copper pipe solder out whatever downstream. That’s why this is a really dumb testing method considering a good one (just testing at the faucet) would have been as easy to do.
  - mlyle 3y ago
    Testing at the faucet is definitely going to end up identical in concentration (plus whatever it picks up in pipes in the house), but not necessarily bioavailability.
    - mattmaroon 3y ago
      I can’t find anything indicating there’s any difference in bioavailability between hot and cold water, or that it’s a concern at all. I’d just assume whichever has less lead in it is what I’d rather drink. If the hot water tank is removing lead from the supply and trapping it, I think I’d rather use it for cooking. (Of course I’m not trying to drink warm water out of the tap in any case. ) And in any case what this study is measuring seems to have little relation to what you actually want you know. But I’d guess you’re right, the hot water tank is probably removing some lead (hence the higher concentration) but not enough to matter much. I strongly suspect the people who say you shouldn’t drink hot water are just parroting something that may be entirely mumbo jumbo, or may be true in some instances for homes with older plumbing but not anymore. I’ve replaced all the plumbing between the street and my kitchen with Pex so there’s no solder after the water heater. (Perhaps hot water does dissolve more lead from that, though I still have a hard time believing it is significant.)
      - mlyle 3y ago
        > I can’t find anything indicating there’s any difference in bioavailability between hot and cold water, or that it’s a concern at all. Bioavailability of lead salts (like that form when you have a lot of hot water, metallic lead, and other contaminants in a tank for a long time) is higher than of metallic lead. Similarly, bioavailability of dissolved lead is higher than that of metallic lead particulate. The mechanism we're discussing is metallic lead particulate sitting in water heaters and dissolving. > I strongly suspect the people who say you shouldn’t drink hot water are just parroting something that may be entirely mumbo jumbo, or may be true in some instances for homes with older plumbing but not anymore. I suspect the people who say you shouldn't drink hot water have looked at the grody water that comes out when you drain a heater that's sat for a long time and see all the sediment and yuckies that accumulate at the bottom.
        mattmaroon 3y ago
        I suspect so too and again, their thinking is obviously incorrect. Those sediments and yuckies were all taken out of the hot water supply, but passed right through to the faucet on the cold side. Every time I drain my water heater, I dumped a bunch of sediment and yuckies down the drain that otherwise would have been in me, if I were drinking from the hot side rather than the cold. The logic you’re describing is like looking at a gross filter you’re replacing and saying “look at all this junk in the filter, I’m never filtering my drinking water again!” Filters look gross when you replace them for the exact same reason that hot water tank is full of sediment. It removed them.