tap water + sunlight = ?

I've read that sunlight can be used to purify water in third world countries of bacteria, by placing the water in the sun for 6 hours. However, I wonder what kind of effect the sun has on a glass of American tap water and all the chemicals and industrial byproducts in it, such as fluoride and xenoestrogens? Is anyone out there versed in chemistry?

I've noticed that when I bring a glass of water outside with me for as little as 20 minutes, the flavor COMPLETELY changes. I know that letting water sit for a full day in the sun can make chlorine evaporate from it, but why does water taste so different after just 20 minutes to an hour? Visually, little bubbles appear all along the inside of the glass, and as far as taste, it tastes sort of...waxy? Can someone who understands the process of solar filtration explain what is going on here, and if I'm somehow making matters better or worse by leaving water in the sun for such a short time? It actually tastes worse, so I am terribly curious.

reply to post by burdenofdreams


Well as far as i know

There are metals dissolved into the water

Such as lead and other metals that are used

When you Boil water they are seperated and evaporate away

Try a room temp glass of tap water

And try a room temp of tap water that was boiled away

The taste is different and i'm sure much better for you

Perhaps the sun kills the bacteria via heat?

The sun evaporates the chlorine out of tap water but the heavy metals remain. Yet chlorine has a strong flavour. To remove all the elements in water you distill it by boiling it and collecting the steam leaving you with pure h2o.

The chlorine can be evaporated off after enough time and some bacteria can be killed by exposure to sunlight, it's the ultra-violet rays that do it. Just putting something outside in the sun isn't a brilliant way to make water safer to drink, it can work but it's not very precise. Destilling is still best.

I am not sure about this. But what I do know is that you shouldn't use a plastic bottle to do it with, due to the chemicals from the plastic heating up in your water may be linked to cancer.

Only those elements with boiling points below the ambient temperature will evaporate out if you just leave the water standing in an open container. These include Chlorine and Fluorine, among others.

The heavy metals won't evaporate out under normal conditions. To get rid of them, you can boil the water and collect the steam (this is distillation). The heavy elements will be left behind in the original container. However, when you boil water, the light elements like chlorine and fluorine vaporize along with it and are present in the steam, so this method alone is not adequate for removing them.

Bacteria can be killed by boiling, UV light (if the exposure is intense enough), or certain chemicals (for example, bleach at the right concentration will kill most of the bacteria but not the person who drinks the water).

Filtration obviously gets rid of any particles too large to fit through the filter.

Decanting can be use to reduce heavy contaminants: let the contaminants settle in the bottom of the container then carefully pour off the top layer of cleaner liquid. This is not a very effective method overall.

The method that you mentioned of leaving water out in the sun is probably not terribly effective. It may kill some bacteria and evaporate some light contaminants, but this method should not be relied upon unless you have no alternatives. Consider that all water in lakes, streams, and rivers has seen its fair share of sunlight yet still has a considerable probability of being non-potable.

If your resources are extremely limited, the best bet is to boil water from a running source. Running water contains less bacteria and heavy metals to begin with, and the boiling will almost certainly kill any remaining biological contaminants in addition to removing lighter non-bioloigcal contaminants by vaporizing them.

Watch Dan Rojas of Green Power Science and he'll show you what you need to do this successfully and distill any kind of water using a Fresnel lens.

Originally posted by Anttyk47
Well as far as i know there are metals dissolved into the water such as lead and other metals that are used

When you Boil water they are seperated and evaporate away

Isn't it the other way round?

When water is boiled it is the impurities and additives that are left behind.

Distilled water is water that has been boiled, then turns to condensation (on a surface) and is collected.

Water can be purified this way and it is why distilled water is used in things like kettles and batteries so there is no build up of things like calcium inside them.

This might help explain:

Water Distillation

I believe the following information may be of use for you:

Solar UV radiation (UVR) is lethal and potentially mutagenic to all organisms at species-specific levels. The stratospheric ozone layer absorbs UVC (

Continued...

Despite decades of study of the effect of near-ultraviolet radiation (NUV) on bacterial cells, insights into mechanisms of deleterious alterations and subsequent recovery are just now emerging. These insights are based on observations that 1) damage by NUV may be caused by a reactive oxygen molecule, since H2O2 may be a photoproduct of NUV; 2) some, but not all, of the effects of NUV and H2O2 are interchangeable; 3) there is an inducible regulon (oxyR) that responds to oxidative stress and is involved in protection against NUV; 4) a number of NUV-sensitive mutants are defective either in the capacity to detoxify reactive oxygen molecules or to repair DNA damage caused by NUV; and 5) recovery from NUV damage may not directly involve induction of the SOS response. Since several distinctly different photoreceptors and targets are involved, it is unknown whether NUV lethality and mutagenesis result from an accumulation of damages or whether there is a particularly critical photoeffect. To fully understand the mechanisms involved, it is important to identify the chromophore(s) of NUV, the mechanism of toxic oxygen species generation, the role of the oxidative defense regulon (oxyR), the specific lesions in the DNA, and the enzymatic events of subsequent repair.

Mutagenic and lethal effects of near-ultraviolet radiation (290-400 nm) on bacteria and phage.

In conclusion:

Exposure to sunlight has been shown to deactivate diarrhea-causing organisms in polluted drinking water. Three effects of solar radiation are believed to contribute to the inactivation of pathogenic organisms

* UV-A interferes directly with the metabolism and destroys cell structures of bacteria.

* UV-A (wavelength 320-400 nm) reacts with oxygen dissolved in the water and produces highly reactive forms of oxygen (oxygen free radicals and hydrogen peroxides), that are believed to also damage pathogens.

* Cumulative solar energy (including the infrared radiation component) heats the water. If the water temperatures rises above 50°C, the disinfection process is three times faster.

At a water temperature of about 30°C (86°F), a threshold solar radiation intensity of at least 500 W/m2 (all spectral light) is required for about 5 hours for SODIS to be efficient. This dose contains energy of 555 Wh/m2 in the range of UV-A and violet light, 350 nm-450 nm, corresponding to about 6 hours of mid-latitude (European) midday summer sunshine.

At water temperatures higher than 45°C (113°F), synergistic effects of UV radiation and temperature further enhance the disinfection efficiency.

Source


Other useful sources:

Survival of Shewanella oneidensis MR-1 after UV radiation exposure.

Applied and Environmental Microbiology

UV light does kill microbials.

So does oxygen.

You can shake or bubble water in the sunlight, and it will over the course of hours purify water of microbials, but other solids dissolved in the water will more or less remain if they aren't oxidized or evaporated.

That's why a fast-moving stream is likely good water to drink, whereas a pond is not.

Originally posted by FarArcher
UV light does kill microbials.

So does oxygen.

You can shake or bubble water in the sunlight, and it will over the course of hours purify water of microbials, but other solids dissolved in the water will more or less remain if they aren't oxidized or evaporated.

That's why a fast-moving stream is likely good water to drink, whereas a pond is not.

Ah well said. You beat me to it, and much splendid summary I must add.

Another thing to keep in mind is that if left open water will absorb CO2 and create carbonic acid. This is the same process that makes all rain water naturally acidic ~ 5-6 pH

So there will also be an antibacterial effect and a taste change independent from the sun. There are other equalibrea that occur in a similar manner so even pure water doesn't stay that way for long.

And dont try this with regular water bottles they leach all kinda of nasty organics when warmed