UKH

Can the hivemind advise on a problem we're having with our home hot water system? There seems to be some sort of biofilm contamination. If we run a sinkful of water from the hot water tap there will be a few small brown tendrils in it that look at first glance like little moss fronds, though they are very insubstantial and I presume they are some sort of biofilm that has detached from wherever it has formed in the system.

Our first concern is, particularly with a (lightly) immuno-compromised person in the house, whether it could be harmful. How would we go about determining that? [update: looks like one can get Legionella home test kits, though I don't know how legit and reliable those are]

Then there is the question of what to do about whatever it is. We don't think it's in the header tank. That has a little bit of sediment at the bottom and I have a theory about where that came from, but the water itself is crystal clear and the tank otherwise spotless. I fear it could be the hot water cylinder (thermostat now set to a supposed 65°C; previously 59°C), but it could be anywhere in the piping of this 1890s house (piping is not that old, but certainly not new). No idea where to begin really (or what to do even if we knew where it was), and we don't have any local plumbers that we particularly trust.

Any ideas?

Caveat that I'm no expert, but could it be from the tap? Do you get it from all taps or just the one?

I'm not able to suggest a source or even a good solution unfortunately but, take great care if you use any form of aggressive chemical treatment as it's almost a certainty that you will have some lead based components in the system and any treatments could result in leaching lead into the water. Although thinking about it again, nobody drinks from the hot tap so if you add it to a header tank it shouldn't cause issues of lead poisoning.

You could replace the open header tank with a pressure regulation valve to supply matching pressure to the DHW, this would need a closed expansion vessel after the valve.  That way you can be certain no more rats are going in to the DHW.

As Jon said, some taps can collect a surprising amount of filth.

could be growing inside taps..

We originally realised the problem because it was gunking up the inlet filter to our power shower. Not sure why I didn't mention that originally (just trying to be concise). We have since also seen it in the hand basin next to the shower - so it's more than just one tap that is the issue. 

I had the same thought as you, and had a quick look at the kitchen sink this morning. No sign of contamination... but also nothing came out of the bathroom sink this morning either, so an inconclusive result so far.

p.s. we first spotted the problem just before christmas because the shower failed completely and I dismantled the filter. Dismantled the filter again last night and there was already some gunk in there (and we'd never noticed problems in the bathroom sink until a few days ago) so the worry is that this is a problem that's rapidly getting worse. Or at least that the deposits have recently started delaminating from whatever surface they have been growing on.

p.p.s. it's perhaps surprising that it's not the kitchen tap which the cat regularly licks (to my unease...) but that's not the one where we have seen the problem.

I can recall something similar, it was something like moss that had caught and established itself in the little plastic mesh piece in the end of the hot tap. Had it in a bathroom sink but nowhere else.

Mark

When I saw your title I thought this was going to be some rant about the good citizens of Manchester.

When I've come across this it has been in the tap.

Do you happen to know of any such chemical treatments? Good point about leaching of lead solder, but as you say it should be ok in the hot system only. Sounds like we should try a treatment of that sort, but I'd have no idea where to begin with looking for one...