Self-filling water bottle turns humidity into drinking water for cyclists | Hacker News Reader

Self-filling water bottle turns humidity into drinking water for cyclists

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76 pointsdavidbarker36 comments

Half a liter in a few hours is way less than a cyclist needs. This is renewable and a bottle isn't but I can pack much more water in the volume of the device and get other water when I stop. If I can't find water maybe I'm in bigger troubles than half a liter can save me from (in a desert, really?). It's not worth it.

However, put a bigger device on a car or on a boat and that can be useful.

until you realize that the drag created by the larger device actually costs more in energy to create the water than other sources.

im curious if this device on your bike would cause you to burn more water than what it produces

I'd imagine the rate at which the water can be collected can increase with more development of the product. Sure, there's a limit at which you're taking all the moisture out of the air, but I'm sure there's more than enough to fill a bottle over the course of an hour of riding.

Where my curiosity lies is in energy consumption. There's a power button on it obviously, so how much power does it use? I'm not an expert in thermodynamics/rates of condensation but I know my dehumidifier is a freakin power hog and it's doing exactly the same thing as this. My guess is that power consumption is the biggest hurdle here.

Products such as these already exist and produce around 30-75 liters/day [1].

[1] http://www.water-gen.com/product-water-generator.html and

>Half a liter in a few hours is way less than a cyclist needs.

I guess you can use it to top up then. e.g. Bring 1 litre instead of the 2 & rely on this to cover the shortfall.

>It's not worth it.

Not yet. Cutting edge near prototype stuff rarely is "worth it".

Cyclists drink half a liter per hour in cool conditions. In the hot, humid conditions necessary for this to produce its maximum of half a liter per hour, they should drink at a much higher rate.

I can see this being pretty useful for long touring rides, where you're riding for a long time but not necessarily pushing very hard.

"After more than 30 experiments, I finally achieved a constant drop-flow of one drop of condensed water per minute"

Guessing the diameter of a drop at 1mm, and assuming it to be cubic, that is 60 cubic mm per hour. Rounding up, we get 1 cc per hour. A U.S. teaspoon is just under 5 cc. Alternatively, get a small cup of water every 24 hours.

There can be about 30 cc of water in a cubic meter of air, so you would have to pump 16 cubic meter of air through this thing and extract all the water to get at 500cc per hour. With a 10 by 10 cm opening, that is a 1600m long column. A bicycle can easily do ten times that speed, so that sounds doable, but that is at maximum efficiency and the article doesn't say he has done that, so I fear that 500cc is wishful thinking.

Why did you estimate the size of a drop as being so small?

Not thinking enough and not googlinh it, I guess.

Looking at the diagrams, it looks like the opening is ~1/4 for air to condense water from and ~3/4 for air to pass over cooling fins to power the condenser, but 1/4 is less than your factor of ten.

I'm guessing this is limited by how much cooling you can get out of it.

Straight from the article:

"Under the right climatic conditions, Fontus can easily produce half a liter of water in an hour's time."

We already know that it can produce half a liter per hour, but those same climatic conditions are when a cyclist needs significantly more than half a liter per hour.

I read that differently. On the one hand, there is the experimentally confirmed drop a minute. On the other hand, they do not state that that half liter has been confirmed experimentally.

I still doubt that number. Looking at http://atmosphericwatersolutions.com/wp-content/uploads/2012..., I see a machine that weighs 38 kg, consumes 373W of power, and produces 'up to 17 liters of water a day'. This thing would be an order of magnitude smaller, and produce almost the same quantity of water. Possible? Maybe. Likely? No. Because of that, I would like to see experimental confirmation of that half a liter per hour before accepting it as a given.

Also, see http://en.m.wikipedia.org/wiki/Atmospheric_water_generator which claims the U.S. army and FEMA use a system that needs a gallon of fuel for 'up to' five gallons of water. If something like this were known to be more efficient, I think it is likely they would use it.

The aquaboy data sheet only goes up to 25°. At 30°, it would produce more than a liter per hour.

In the conditions where it produces half a liter of water per hour, you're going to need more than that just standing still.

I wonder what the power requirements are,

The cooling system has to be cooling the air that passes through it down to the dew point, if the ambient temperature and the dew point are too far apart, it's going to consume too much power to be practical.

It also looks solar powered-only, so its efficiency is not better when the dew point is closer (night/morning).

Linking a small solar cell (I would say ~1W from the shown surface) to a Peltier element (known power hog, a really small one takes at least 4W) is not a solution for efficiency.

Wolfram alpha says it takes ~1.3kj to change the temperature of 1m^3 of air by 1 degree C. Obviously this will vary enormously with temperature and humidity, but it gives us a number to work with.

Wikipedia, and a post by 'someone' tells us there is ~30cc of water per cubic meter of air at 100% humidity and 30c. (This could be a reasonable set of envoronmental conditions in Washington DC for example).

The mass of water in 100% humidity air is

28c 27.22g http://www.wolframalpha.com/input/?i=mass+of+water+in+1+cubi...

30c 30.34g http://www.wolframalpha.com/input/?i=mass+of+water+in+1+cubi...

So we can extract ~3g, or 3cc of water from saturated air, with the use of ~2.6kj (assuming 100% efficiency, which is unlikely)

Some of the highest power density batteries I've handled are 5 cell, 5500mAh li-poly batteries for model aircraft use, with a total energy capacity of around 180kj,

Or ~ 200g of water.

I think I'd rather carry a water bottle.

Here in Italy, every little town has at least one water fountain; often near the church or town square. Even in the summer, if you're good about stopping often, you could probably get by with just a small water bottle.

For some reason I wouldn't want to drink the water after biking through a swampy area.

If you cycle through areas with a lot of traffic, could the water end up contaminated with vehicle exhaust?

I'm pretty sure most harmful exhaust would be more harmful when breathed in, than when drunk?

Sorry to be pedantic, but if you are pretty sure, then how come you end your sentence with a question mark?

You don't sound sorry.

I didn't hear any sound at all.

In the same concentrations, I'm sure that's true, but the collection process will also concentrate pollutants quite a bit.

The lack of electrolytes in the water could actually be extremely dangerous for a biker. I don't see how this issue is addressed.

Same with lack of food. Solution: carry it with you.

it needs a piss recycle system that humidifies the air it takes in, tada, faster filled bottle.

and has all the electrolytes...

Thats genuinely impressive. I'd be concerned about the lack of electrolytes though? Presumably cyclists would need to top those up too.

If you're concerned about electrolytes, I just invented a much better solution - just wringe your t-shirt after a ride and pour the water into a bottle, you'll have all the ions back

I had a similar design but it was fixed use, like a wind mill but produced water. Same concept.

It's a great idea, but it's going to need a lot of dev to become a product.

Fantastic! One step closer to making Fremen and Dune technologies reality!

Kickstarter plz.

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