Sun water heaters...not roof.

[Archie]

Hi...gotta problem....are sun cookers safe, normally get 15 litres of hot/warm/tepid water per day, but concerned about bugs, would you think I need to measure the temperature each time.
Use it for personal washing, washing the dishes and clothes soaking.
Thank you..Have registered as newbie and said hello, may not have 'took'. Will do it again. From Norfolk UK.

[Muddypause]

Hello, Archie,

When you say a sun cooker, do you mean something that cooks food by solar heat? If so, I reckon Nev (Wombat) will be your man for advice.

Or do you mean a solar water heater? And you are concerned about stuff like legionella?

According to Wikipedia, legionella is killed by temperatures above 55C (for 5 - 6 hours; higher temps for quicker eradication), and I have read elsewhere that copper piping is also somewhat bacteriacidal. Most domestic hot water systems are set to heat the water to 70 - 80C to deal with this problem, but of course that is only tank temperature. I've also read advice that if your system doesn't regularly get up to these temperatures, it may be a good idea to heat it by other means every few weeks.

But I've also read that legionella is only a problem if your immune system is compromised, or you are elderly (what counts as elderly these days?), and that if you take precautions (no open tanks, don't let water stagnate, etc), then you may never have a problem anyway.

[Wombat]

what Muddy said, but more detail on the sun cooker please.........

Nev

[Archie]

Thank you for replying....the sun cookers are two 8litre stainless steel pots , painted black, with lids and stand , in one case an old cast iron washing 'copper'. Suppose this was lined originally with copper, now lined with cooking foil. The other is a small tin bath, again lined with cooking foil. Both with storage heater bricks in the bottom to catch and transfer heat.Covered with polycarbonate sheet.
The water does get hot/warm/tepid according to the sun, and on a very hot day get two loads. Covered at night, opened up early, gets sun all day.
Use fresh rainwater each day, and pots are cleaned easily. The rainwater is filtered, to what level, I know not, before and after cooking .
Legionella is the worry, should I be using tap water, should I boil the already hot water. Picture to follow.

[Archie]

Here is the main cooker, exclude the beer barrel, that is another project

[Muddypause]

Ah, that looks interesting. Probably not the most efficient way to catch solar energy, but simple and cheap.

I'm certainly no microbiologist, but my understanding of the issue is that legionella can be anywhere around us all the time, in the air, the soil, as well as water. But it only becomes a potential danger if conditions allow it to multiply and form a colony.

As you replace all the water every day, and the pots can be easily cleaned, I guess this would not be a problem. If it was a system that was wet all the time, it may become so under certain circumstances.

But as it's rainwater you are using, there could be all sorts of other stuff in it, partly depending upon how you capture it and how well it is filtered. If it's simply roof captured water, speaking personaly, I might be inclined not to wash the dishes or my self with it (nor to use it for drinking or cooking).

[Archie]

Thank you for the input, Muddypause, will probably go over to tap water.
and pay more attention in tepid times.
But the water on a sunny day is more than hand hot, and very hot sometimes. Perhaps boil it when in doubt. Another expense..

[Archie]

Do you think sterilising the dishes after washing would do the trick. In a microwave oven, maybe even the water .

[Muddypause]

I would think the risk of legionella in your setup is very small - I don't think, from what you describe, you could harbour any breeding colonies of it in your pots. My comments were more to do with the muck (including bird droppings, rotting leaves, moss, lichen, insect life of all sorts, and who knows what other stuff) that is likely to be included in any water that is captured on a roof.

I'm not trying to be alarmist, but I think I'd feel a little uncomfortable using dishes that had been washed in it (have a look at what collects in the bottom of a water butt - or, indeed, in the guttering). If the water is filtered well it may be OK, and your practical experience of your setup may be something you are comfortable with.

Isn't there some sort of ultra-violet water treatment that kills any bugs in it? Nev, do you know anything about that?

[Archie]

Thank you for your advice, I reckon tap water would be safest. Pity because rain water is so soft. Perhaps one pot with tap and one pot with rain, and boil the latter when warm or tepid, and further research into filtering. Muchas Grassiuss.

[Wombat]

G'Day Stew and Archie,

There are 240v powered UV water sterilisers which work on the supply being run past the light in a thinnish film.....I have data on a homebuild which i will dig out and link to.

I understand Stew's concerns about microbilogical contamination, but people have been drinking, washing etc with tank water here for a couple of hundred years. If you wanted to really make sure there are filter systems and coupled with the UV the water would be damn near sterile!

Ah yes, here it is!

http://rael.berkeley.edu/old-site/uvtub ... roject.htm

Nev

[Muddypause]

people have been drinking, washing etc with tank water here for a couple of hundred years.

I'm sure that's the case in many parts of he world, Nev. When I was a boy, the cottages where my grandparents lived had rainwater tanks that would be pumped by hand, or water that was piped in from a nearby artesian well. The tank water was definitely not for drinking, and we were given dire warnings about it.

I'm not trying to say don't do it, rather than do it with a certain amount of awareness.

[Archie]

Thank you, Nev...some report, and at $41 wont break the bank.

[Wombat]

No worries Archie!

Point well taken Stew!

Nev