They are essentially the same thing, except with a semipermeable membrane instead of a filter per se, acting as an extremely fine filter. Also, there are no chemical reactions between the membrane and the solvent or solute, as there may be, with, say, a charcoal filter, which chemically binds organics. Reverse osmosis is usually slow as the dickens, and takes lots of pressure to reverse osmotic pressure, but it results in an extraordinarily pure product.
Osmosis acts through a semipermiable membrane, I accept this. But what is a semipermiable membrane? From my comprehension it is a filter - ie. some things can pass through and some things cannot. Forcing it through due to water pressure is not osmosis–it is filtering.
Again sorry for the hijack but this is the first question I sent Cecil and he declined to answer, and instead directed me to this board–now I am addicted and want an answer, dammit:)
A membrane can be a peice of plastic with microscopic water molecule sized holes…or some material that is like that. So a membrane lets things through little holes in a material. Since things like to go from regions of high concentration to regions of low concentration, and even out, getting things to go from a low concentration to a high concentration requires energy in the form of high pressure. This costs alot of energy, enough to make the process only used for things like bottled water, and water in places that are hard up for other sources. The advantage is that the membrane should last a very long time.
A filter has loose stuff packed, with tiny spaces inbetween. A filter lets stuff get through the cracks. The filter material is often affected by the impurities, as filters usually work by absorbing them into their structure. So usually you have to reflace a filter after a time, because it gets clogged with gunk. The advantage is that it is relatively cheap, and gravity provides all the pressure you need. Another disadvantage is that it doesn’t remove impurites as well as reverse osmosis.
I think that you and I disagree with the definition of a filter. I am not trying to understand the different ways water is filtered. Certainly water is filtered through charcoal and other manners of “cleansing”. I am more interested in the osmosis question–osmosis happens as a passive occurence, as you said
By my definition as soon as you apply energy it ceases to be osmosis and starts to be filtering.
It’s not osmosis! It’s reverse osmosis!
Sorry I can’t offer you micro-elves separating the good molecules from the bad, but RO is just a highly specialized form of filtering. 
AFAIK, most bottled spring waters market regard themselves as superior because treatment is not necessary - the water comes out of the ground with a level of purity acceptable both to the pallete and to food & drink regulations.
Holy crap, people are actually getting upset over this?
It’s WATER! In some places, it tastes like crap! In other places, it doesn’t! Where it does, people buy bottled water that DOESN"T taste like crap!
Note the “tastes like crap” part. Ever been to Hayward, just south of San Fran? Water tastes like crap, there! Ever been to the San Fernando Valley, more south of San Fran (much more)? Waater tastes significantly less like crap!
Note that “tasting like crap” is also very subjective!
Sheesh. People that get their little strawberry-emblazoned panties in a knot over this really need to get their grubby 'lil hands on some Valium…
According to Chemistry 101, wateris H2O-and whether is comes from a contaminated spring in France (Perrier), or a reverse-osmosis plant in London (Dasani), it is all the same! Plus, statistically, the water you drink today once passesd through Julius Caesar’s kidneys!
Do ya think I would get anywhere marketing GANGES RIVER WATER? (Makes your hjourney to Nirvana shorter! 
Can I ask a question?
What does anyone care what I spend my money on? Filtering my own water in a Brita pitcher does not work for us in our household (due to small children in the fridge, too much stuff in the fridge, and general laziness. A pur filter on the sink doens’t taste good to us (and we don’t change the filters often enough).
Yeah, I can buy a big two gallon jug of cheaper water (Chippewa is sold all over my area), but I prefer the taste and convienience of little bottles of Dasani (Chippewa isn’t that much cheaper in little bottles - the grab and go kind I like for convienience - and as I prefer the taste of Dasani that is what I buy). And, it isn’t breaking my budget to pay Coke for it (and I own stock in Coke anyway, so I, in some small way, get some of my money back).
There are a lot of things in life that I wonder why people spend a lot of money on them and I think are of questionable value. My brother in law likes $75 a bottle Scotch. All tastes like lighter fluid to me, might as well get the $7 bottle - but to him it makes a difference and he enjoys it. My dad buys Grey Goose vodka. One of my coworkers swears by moisterizer that’s $50 for a little tiny bottle. Another drives a BMW. Its their money.
Well, I just finished reading this thread while finishing off a bottle of San Pellegrino. San Pellegrino is naturally carbonated spring water from the Italian Alps with additional carbonation added. It’s mighty tasty stuff but I just don’t think there is enough natural spring water in the whole world for everybody to drink. Hence, I think filtered tap water is a good alternative. Especially for those who don’t like carbonation. Many spring waters have some natural carbonation.
Of the JILLIONS of H2O moleculesI just drank…how amny passed through Julius Caesar?
The thought of drinking recycled pee annoys me! 
I almost always drink just water. So much so that we put in a big ol’ reverse osmosis filter. It’s big enough to filter our ice machine and to cook with. It has made me a water snob, you could say. For those of you who think regular tap water is ok, you either haven’t had my water or you don’t drink enough of it! 
Dasani is made for people like me:
I’m away from home but am thirsty. I would infinately rather drink the Dasani instead of the coke, even the price is the same.
Turns out you’re full of crap. An entire industry exists around the going-into-the-wilderness and the sucking-up-of-purty-little-streams-of-water. And don’t try to weasel out and pretend municipal water has the same source as bottled spring water: it’s usually taken from rivers, lakes and dams fed by run-off rainwater, which is quite different to spring water bubbling out of the fucking ground.
“Still water” is an antonym of carbonated water, which is an important product distinction to make. So essentially you’re arguing marking folk have chosen “pure water” to evoke a natural spring image. I’m not sure that washes.
“Distilled water” would be misleading.
I’m with Ferrous, incidentally. If I can’t carry around a bottle of water from home, I’d much prefer to pay for overpriced bottled water (be it tap water or spring water, I don’t care) than overpriced, sugary, fizzy crap in a can. I suspect obesity rates would be lower if more people did the same.