avoid legionella in solar hot water?

What do you guys do to avoid legionella in your hot water systems?

Nobody is rushing in to answer. Maybe if you gave us some more background about your hot water system, we could come up with ideas for you. The three common methods for slaying bacterial pathogens are chlorine, peroxide, and ultraviolet -- do you have one you are leaning toward?

We have a well and a cistern (we are going to collect rain water - the gutters should hopefully be in place before the rain starts. The water is clean - no need to clean it before consumption.

Our water heating will be a passive solar ciffon using cobber tubing, and a wooden frame with a plastic roof in front.

The cistern is made from rocks and half burried in the rock around it, and has a big carob tree growing on the south side of it. I have no doubt that it will stay cool through the summer months.

The hot water will be very hot in the summer - I am sure - so that should kill the bacteria. We live in the south of Spain, Mediterranean climate (zone 8?). But people who have solar heating says that they don't have any hot water in the morning during winter if they don't have an electric backup. So my problem is: How do I make sure I keep the temperature high enough to kill legionella in the hot water tank during winter?

As far as I know temperatures above 60C (140F) is what you need to keep legionella at bay, and as legionella is air borne there is no use in cleaning the water, it is all about temperatures. So my question is how do people ensure that without some electric control system?

How about a UV system on the pipe coming out of the tank?

I would guess that most systems deal with this by having a backup hot water heater set to 160. That way, when the sun is out (and most of the summer), you get all the benefits of solar, but in the times when there isn't enough, the backup kicks in and keeps the water hot enough so that the legionella aren't a problem. That said, I don't know of any alternates to what John had mentioned. OK, well, I do know of copper & silver ionization, but my understanding is that's a hefty investment that only hospitals and large buildings entertain, and it certainly requires electricity, so I figure that one's pretty much ruled out for you.

Backup system for winter--could be electric, gas, or wood. Or you need to increase your collector size/efficiency to get enough heat in the winter and shade it back in summer so it doesn't boil.

Say your water heater tank only get to 120F in the winter, that temp is more than hot enough for use but not hot enough to kill legionella, so the solution is to use UV to kill the microbe as they move from the "hot water tank" to the faucet/shower head. I have drank/showered/bathed in unheated/untreated roof catchment water for months/year and never got sick. But that could have been because the water was not heated (slow growth), or I just got "immune" after getting sick once when I was a young.

It takes time for bacteria to multiply. Cycling the system above the lethal range is an effective method of control.

From Wikipedia --- * Above 70 °C (158 °F) - Legionella dies almost instantly
* At 60 °C (140 °F) - 90% die in 2 minutes (Decimal reduction time (D) = 2)
* At 50 °C (122 °F) - 90% die in 80–124 minutes, depending on strain (Decimal reduction time (D) = 80-124)
* 48 to 50 °C (118 to 122 °F) - Can survive but do not multiply
* 32 to 42 °C (90 to 108 °F) - Ideal growth range
* 25 to 45 °C (77 to 113 °F) - Growth range
* Below 20 °C (68 °F) - Can survive but are dormant, even below freezing

The whole article --- http://en.wikipedia.org/wiki/Legionella

I got quite sick 5 years ago. --- This is copied from another thread from 17 months ago . It was the worst health scare of my life. --- I infected myself with this 3 years ago. I was in the habit of showering in buildings that I was demolishing up to a week after the power was cut. Often the temperature had taken days to cool and thus spent too long in the critical temperature zone. If you ever rent a cottage or motel room where the tank is turned off, wait for it to totally recover before showering. A bath is safer since inhalation of vapour is how you get it. This was the biggest health scare of my life and I no longer shower at job sites when the power has been cut.

Because of this risk all of my alternative hot water both current and planned is of the batch type. Water that is only held for the day does not have time for a population explosion of any unwanted organisms. Wood fired hot tubs often go through large temperature fluctuations. This helps to ensure that they are not overrun with organisms that only thrive within a narrow temperature range. The same water held at a constant 105 F would need chemical treatment to remain "safe".

In my case, everything that I did contributed to my chances of being infected. I not only showered in the infected water but also rinsed my mouth and nose, gargled etc. My paranoia about asbestos, rat feces and other contaminants that I regularly encounter at demolition and renovation projects led me to purposely snort water up my nose and blast it out again several times a day. I was also in the habit of filling a tree sprayer with water and spraying the room with lots of mist for a swamp cooler effect.

Vaporizers have been implicated in infecting babies. Parents assume that hot water is more sterile so they use it in the vaporizer. Usually the cold incoming water does not contain high levels of legionella.

The bio-film that accumulates on tank surfaces and bottom sediment can be many times higher. I often showered in water that was slightly cloudy since the water had been turned off and on with pressure surges and often the hot water tank had been disturbed. I often shook tanks to dislodge bottom sediment so that the reused tank would last longer at the new location. The highest concentrations of legionella have been found in the scale and sediments that accumulate at the bottom of tanks which can be quite a bit cooler than the top of the tank. Probably the most dangerous thing I did was to continue using water from the tanks after the water was cut off at the road by gathering it from the bottom drain spigot. This water often contained bits of bottom scale. I had many luke warm baths from tanks that no longer had water pressure.

Dale - what you say makes me very much calmer The other day I dropped a rock on My finger on to another rock (yes auch!) and I ran up to cool it - the hose had been lying on the ground all morning - and it took a loong time for it to get cool - ie the water lying on the cold ground on a winter morning was around 30 - 38 C (86-100F) - just from lying in the sun. It will get a lot ware in the passive heater. Many many days it will still get above 60C mostly it will be above 50C. I will try to do some sampling of data once the heater is done and see how often we will need to heat the water.

Thak you!

Edit: from 30 to 30-38C

Dawn Hoff wrote:Dale - what you say makes me very much calmer

I often have the opposite effect on readers.

Big apartment buildings and commercial buildings usually have boilers that get well above killing temperature. The water goes through a mixing valve where cold water is added to bring the temperature down to a desired temperature before it is piped to users. Without the mixer, scalding would occur.

In temperate climates, both streams are safe. One has been sterilized and the other has never been warm enough for bacterial populations to explode. In tropical areas where groundwater stays warm all year, legionella can be a constant threat unless all of the water is treated in some way. If you visit a hot spot, it's better to bathe than to shower. Don't snort it up your nose.

In the sum er we usually do bare in the pool (we won't have one next summer though, not top priority). But I will watch the cold water when we get there.

If your water source is clean enough, you could make use of the fact, that legionella (as all bacteria) need time to grow/multiply. If your water is heated in a short period of time, they don't have the time to reach a population big enough to be dangerous for you. To make sure the water you get in contact with (Showering, drinking etc.) is heated quick enough, you have to keep it cold as long as possible. This means you need a heat storage (Hot water tank) wich is heated from your solar energy source and a separated water pipe which is heated from the heat storage via a heat exchanger. You should make sure hot water and use water never get mixed. Plus - just to be sure, you could chlorinate the heat storage (its closed loop, not water exchange) just in case of a small leakage.

I think we get an old electric heater from a friend (the electricity is gone, so it is basically the water tank we get) - and I think it works the way you describe.

If you're using copper piping, you shouldn't have to worry about legionaires' diesease due to the oligodynamic effect.

http://en.wikipedia.org/wiki/Oligodynamic_effect

Copper pipes are required in the United States, even if it's only the first few feet of the incoming water service, so legionaires' diesease is almost unheard of here. Copper ions are vicious against legionella, whereas it's been shown that legionella can survive up to 24 hours inside a gallon jug of commercial bleach. This is not why copper pipes are required in the US, it's a useful side effect of decades of corruption within the construction industry, but a win is a win.

Great! My husband is building it as we speak - in copper piping, primarily because it has better heat conduction