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At 18:14 25/08/02, Peter Macinnis wrote:

Surely there is some simple way (solar still or whatever) of delivering low-impact clean water, free of infection, free of toxins and poisons? I rather like the idea of a solar-powered centrifugal pump pushing water through a chamber where (not-yet-invented) UV-emitting LEDs kill the bugs. That would be a start, but I suspect that a solar still would be needed  in SOME places, because of dissolved unpleasantries in the water.
 

Chris Lawson replied:

Even a sari or a piece of denim, slung across the mouth of a water-jug, takes out most of the protozoa . . . It is amazing how lo-tech you can be to get clean water. You don't need treatment tablets. A charcoal filter will fix most problems. A plastic bag and some rubber tubing can be a very effective solar still.
 

I write to support Chris' view.  Probably the most important part of providing clean water is to get people  to use it.  The concept of "clean" seems simple enough, but for those with  little understanding, this means visually clean, which is a poor way to  assess the quality of water intended for ingestion or even washing.  Even getting people to line up and use a well, instead of going to the river  and letting it settle in the bucket for a while, is a bit of an achievement. 

Toby Fiander  (who once had an illustrated booklet on constructing water wells translated into Pidgin)
 

Ray wrote, in reply to Peter:

I wonder if you jest Peter?  The filtering potential of woven cloth may be good for grit, but 100 micron?
You might be right, but I doubt it.

Even if it might filter out amoeba, and perhaps even nematode eggs, its efficacy for 10 micron and less (bacteria and virus) would be poor to say the least.

Skip the denim.  Try coffee filters...
I've no objection to distillation, provided the still is kept clean. (sterile and free of lead piping recycled from the local tip)

Right... well, the next time I am in a village, Ray, I tell them to use coffee filters for water and while waiting for it to pass through let them eat some cake.
 

Gerald replied to Ray:

You are looking at the filtration in a purely mechanical way, bacteria have an affinity for surfaces or various types and will attach themselves quite firmly to fabric substrates so you have to consider this as an additional factor, an aspect to which I believe Peter was referring indirectly. I would think cotton fabrics would be highly attractive to bacteria and fungi as a source of food.

i posted a while back on using a sari to strain water -- Ray questioned whether it would get bacteria, and Toby and I both pointed out that I was referring only to propotozoa.

I have just come across this slide:
http://www.nsf.gov/od/lpa/forum/colwell/rc02abelwolman/sld028.htm

Which makes it clear that Vibrio cholerae levels can also be reduced.
Comments?

NB: look at the URL, and realise that this is very high quality stuff, not likely to flake.
 

Chris Lawson responded

This is a very interesting finding because there's no way a sari cloth would ahve a fine enough weave to filter out bacteria. Presumably what is happening is that the cloth filters out larger particles that carry bacteria on them.

Thanks Peter (and you weren't kidding about complexity were you?), but I now accept that a sari is much better than nothing -I mean, for filtering water. :)

I think it was Gerald who informed us, and confirmed an extension to cloth efficacy beyond the protozoan of your initial message, with mention that bacteria often have an attracting affinity for natural fibres.

Thus, I have most humbly pulled my head in.
 

On 5/9/2002, Julia mentioned...

I am fortunate to have my own rain water...

Margaret replied:

Fortunate, indeed :-)

A Victorian study a couple of years ago looked at water quality in rainwater tanks on 100 farms. The researchers concluded "There was no obvious relationship between drinking water quality, householder knowledge, maintenance practices and drinking water-related health risk on farms."

Other findings:

* coliforms were present in 52 tanks and E. coli in 38

* seven households reported minor illness in the previous three months, and two reported gastoenteritis

* none of the households had their drinking water tested regularly

* 86 households did "some" tank maintenance (removing the dead pigeons, etc, presumably)

Here's the reference: Glenda Verrinder and Helen Keleher, "Domestic Drinking Water in Rural Areas: Are Water Tanks on Farms a Health Hazard?" in Environmental Health, volume 1 number 3, 2001. Published by the Australian Institute of Environmental Health

Cheers to that, eh?

Toby added:

Water quality is a vexed issue, but based on the study Margaret refers to and a number of others over the years, it is probably better to use a reticulated supply which is operated by a major authority than to collect rainwater... at least they are (sometimes very) aware of their legal responsibilities to provide a good quality supply in accordance with NHMRC guidelines.

However, if you like unfiltered undisinfected water and you are careful and do not live in a city, there is probably only minor risk.  Some people like the taste.

I don't like wildlife in my drinking water.  Water should be filtered, fluoridated, chlorinated (sic) and have its pH adjusted prior to delivery to my sink at a suitable pressure for use.  I delegate this authority to others who take responsibility for it for about $1.00 per tonne, including taking it away again when I am finished with it and disposing of it without polluting the environment.

I don't much like bottled water - the way you get it at the garage when you are filing up with petrol and feeling thirsty costs about 4000 times the price of the water from the tap.

Incidentally, tank water is about four times the price of tap water, assuming you value the maintenance continual work at zero and cost only the components that are outgoings and stretch the life of the paper filter elements as far as possible.  On the other hand, most of the costs are sunk costs (oops), whereas with tap water most of the costs are on-going costs.

Tank water is fine if don't mind the risks.  The dead animals and their faeces are not what I like in my water.  Constantly patrolling the catchment, cleaning out the tank every year and scrubbing the inside of the pipes every few years like the water authority does would be a good start, but you need more than just a tank to provide a realistic alternative supply to reticulated water if it exists.

Sticking a paper filter on it would help and dosing it with chlorine would help too.  You still don't get a water as good as what comes through the tap.... it ain't perfect, but it sure is good value for money.
 

Peter posted, further to a reprise of filtering through cloth:

> That would make sense -- Cryptosporidium spores also travel inclumps,
> I was told when Sydney was having a scare a while back.  Do other
> pathogens clump?  Some of the cocci form chains . . .

I did some more digging, and found this, which makes even MORE sense,
at http://www.tve.org/ho/doc.cfm?aid=588:

"The bacteria are normally found associated with free swimming, tiny, microscopic shrimp-like animals called copepods. Each copepod carries thousands of cholera bacteria in its gut and on its surfaces, and ingesting a small number of these creatures containing the cholera bacteria when drinking or eating uncooked food, such as fresh fruit or salad, can cause cholera. Plankton blooms occur in spring and autumn in Bangladesh and each bloom is invariably followed by an outbreak of
cholera."

OTOH, certain copepods have been proposed as essential additions to water tanks as they knock off the dengue virus by eating the early stages of Aedes sp.

I am out of date on the actual surface mechanisms but bacteria and protozoa have millions of tiny fibrils extending from their surfaces and these are actively used to catch hold of all types of surfaces including each other. As to the effects of electric charges which no doubt also exist I leave for others to answer. They can really hold on very tightly when it suits them, Vibrio cholerae comes to mind.

I have an image of a mass of biofilm in an air conditioning heat exchanger in a condition which should never arise. I will send a copy to Barb for the Website. The important thing to remember is that as the surface is colonised and the biofilm increased in depth it creates a zone of both growth and death among the colony as you would expect. This creates a pool of recycling nutrients for them at concentrations with are much higher than in the surrounding fluid medium therefore surfaces are attractive places to be. The biofilm become quite a community of organisms many with serious pathological potential.

NS published an article on biofilms a year or two back you might like to look it up.

	An illustration of the top of a corner of a cooling tower at a metal fabricating plant in a terrible state. Although the owners had tried various treatments and services ineffectively the biofilm still built up quickly which says something about the effectiveness of the independent service used. This tower would almost certainly have been heavily contaminated with Legionella sp. and others.
	This image shows a manifold (one end chamber) of a horizontal heat exchanger on a building air conditioning system. The upper half shows the end plate to which the horizontal copper tubes are brazed and through which the cooling water from the tower passes. The water is passed along one half, indicated by the open tubes, and back through the opposite half which in this shot are all virtually blocked by mineral/biofilm growth and corrosion. This view was taken after the chamber had been preliminary hosed out. A disgraceful but not uncommon situation. The outer surface of the tubes and behind the end plates is a separate closed circulation of refrigerant which transfers heat from the building to the water as it passes back to the tower. The lower half of the images shows the residual  mineral/bioflim material which is a hard porous cementicous permeated by biofilm strands living and dead. The lower layers are recycled through energy extraction until the deposit achieves a density similar to ceramic china and forms a stratified structure of visible layers similar to the rings of a tree. Growth mostly occurs at the free surface where the microorganisms proliferate and the calcium and sulfur and carbonate are deposited. The composite material is about 45% organic in composition despite the apparent density of the material.
	This image shows Hex1 BA after cleaning and surface coating is complete. It is not unreasonable to suggest that with a good maintenance program this condition can be maintained relatively easily and at a cost which is more than recovered in energy savings alone.
	This illustration shows the condition inside the manifold of a large heat exchanger at a food factory of all places. The close up on the right shows the proliferating multicoloured community of organisms making up the biofilm. The frame on the left gives a view of the chamber, almost 2 m in diameter, after one irresponsible flush with hydrochloric acid. Note the kilos of copper metal stripped from the tubes and deposited all over the place just to remove some biofilm which should never have reached such proportions in the first place.