LA is dumping millions of plastic balls into its reservoir to tackle the drought | Hacker News Reader

LA is dumping millions of plastic balls into its reservoir to tackle the drought

sciencealert.com

51 pointschris-at73 comments

They're not dumping plastic balls in order to tackle the drought, they're being dumped because the EPA mandated that all reservoirs be covered. Direct sunlight will cause bromide and chlorine in the water to mix into bromate, a known carcinogen, and the EPA wants to prevent buildup of this compound in the drinking water supply. Covering the reservoir with a tarp is too expensive (costing over $300 million) and plastic balls are a much cheaper option. The evaporation reduction is a secondary benefit, not the primary one, and the article title should reflect this.

There's much better coverage of this story here [1] and here [2].

[1] http://www.npr.org/sections/thetwo-way/2015/08/11/431670483/...

[2] http://news.nationalgeographic.com/2015/08/150812-shade-ball...

doesn't the plastic + sunlight + heat combination release dangerous chemicals in the water?

also, why are they black, doesn't that attract more heat?

That's also what I was wondering. Touching something wet, being warmed by the sun, and all that, can't be good for the black plastic.

That's what I thought, too. Shiny silver balls would reflect even more light, and look super-cool!

And they'd sink

Why would they sink?

Being balls, they would also reflect that light into the water

Actually white balls probably would be better. What you normally reach with specular reflection is around 80% reflectivity. With diffuse reflection (white colour) you can get into the 99.x% range much more easily.

They don't care that much about heat, they care more about sunlight not reaching the water, which black balls are more effective at.

why would black be better than white?

i remember an article stating that the melting ice at the poles is accelerating global warming because the white of the ice used to reflect the light coming towards the water

Because white reflects, black absorbs. White balls wouldn't reflect all light upwards. To put it another way, if you were in the water, looking at the surface, which would be brighter? White balls or black balls?

makes sense :)

The problem is specifically the ultraviolet photons in the sunlight, which photoactivate the reaction between bromine ions and ozone to form bromate [1].

The visible color shouldn't matter as much as strong absorbance or reflectance in the UV band. I would guess that they're using a plastic that absorbs UV, or contains a dye that does so.

1: http://www.ncbi.nlm.nih.gov/pubmed/18290477

Was the article edited after you read it?

> And the primary reason for deploying the hollow balls is more to protect the quality of the water rather than to simply stop it evaporating. In the reservoir water, the naturally occurring bromide was mixing with sunlight and chlorine (added to disinfect drinking water) to create dangerous levels of the the carcinogen bromate. Shade balls should stop that harmful chemical reaction from happening at a large scale, and of course by deflecting the Sun's rays, they also keep more of the water in liquid form.

Wouldn't it make more sense to add the chlorine after the water is drawn from the reservoir?

Doesn't that fix the bromate problem at the root?

Just a guess, but maybe chlorine needs a good amount of time to be effective, and the transit time from reservoir to tap might not be enough

Why not use ozone to teat the water. It's a better solution that chlorine, even more effective to kill bacteria.

Why not, indeed...

Bromates are formed many different ways in municipal drinking water. The most common is the reaction of ozone and bromide.

Source: https://en.wikipedia.org/wiki/Bromate

I would guess that having loads of dead algae in your drinking water is not much better than live algae. You want to keep assorted gunk from having a chance to grow in the first place.

But certainly the water is filtered before reaching homes, considering it rests a long time in a open reservoir. So you could remove the dead algae. Still, they certainly have a "better dead" approach, wanting the reservoir to be a dead pool instead of a living ecosystem where they'd have to monitor what is growing and how dangerous it might be.

It's interesting to compare different systems. Here's one for a small part of the UK. Our tap water (from thefaucet) is vety high quality.

http://www.thameswater.co.uk/cycles/accessible/water_treatme...

The last stage of the process is to add chlorine to the water.

Is there any reason why you guys don't have your reservoirs underground? It seems to me that that would solve a lot of problems.

They're pretty hard to dig. Outside resivour can be made by damming a mountain valley and filling it in.

They have space, and they conceived this system, like many others, thinking of what was the easiest thing to do, disregarding a low-maintenance approach.

Well, there is a difference from "we do this" and "we have been mandated to do this", whatever the reason "to do this" might be. I guess that explaining they were forced to cover the reservoir makes me appreciate the solution even more: given an order, they found an intelligent and efficient solution.

The article says all of that:

> And the primary reason for deploying the hollow balls is more to protect the quality of the water rather than to simply stop it evaporating

> Covering the reservoir with a tarp is too expensive (costing over $300 million) and plastic balls are a much cheaper option.

This is what I don't get in this story. How on Earth are plastic balls cheaper than just covering the thing? One would think that a tarp would use less material and be easier to manufacture than the equivalent number of plastic balls.

EDIT: Thanks for all your answers. I guess the heatwaves we have right now in Poland are negatively affecting my imagination :(.

I'm guessing the problem is managing a tarp that big.

> One would think that a tarp would use less material and be easier to manufacture than the equivalent number of plastic balls.

How do you suspend the tarp? What about when it rains on the tarp, increasing its weight substantially? Repair the tarp when sections get damaged? UV resistance over its lifetime?

Using barges/boats and dragging it from shore-to-shore is very slow going, and any suitably durable tarp (i.e. waxed canvas or some plastic) is going to be HEAVY.

Repair, weight, suspension and deployment seems like the hardest issues to tackle.

The tarp would ideally need to be reflective, like a white roof on modern buildings. The rain issue is the easiest one to solve, since the tarp could be slightly perforated to allow drainage.

I wonder if a permanent structure over the lake would be easier than a tarp? Like literally building a roof.

Either way the balls seem like a solid approach.

How would you make a lake-sized tarp? How would you deploy it, repair tears, etc. You can just make balls with a press and dump some more if they get damaged.

Will tarp be a single piece or multiple pieces? What's the weight of the tarp? how do you make sure it's on the surface? Or do you need a support structure to keep it above the surface (say a meter etc.)? Will it have holes to drain? Will holes be sturdy enough in the long run? etc...

I was thinking why they use ball form instead of something sheet-like. E.g. thin pancake - it will have same properties as the balls but will cover surface more efficiently, if you count material.

I guess that the area to cover is very wide, and having a tarp that size can be expensive. And then you still have to manage it in order to tolerate the weight of rain water, leaves and sand that would eventually gather upon it.

Went to the second link, and got the real story. It was an isolated, rare problem. The EPA mandate makes sense. Only these three lakes had high levels of bromate in 2007? I was picturing my beloved lakes filled with plastic.

"reservoirs exposed to sunlight are now rare. The area's reservoirs -- Silver Lake, Ivanhoe and Elysian -- first registered elevated levels of bromate between June and October 2007.

But state health officials said the dangers were minimal because bromate poses a small cancer risk only after consumed daily over a lifetime."

This may seem like a silly question, but...

Why on earth are you chlorinating the water in the reservoir? I've never seen any other country that does that. Isn't it a really, really terrible idea? Environmentally ghastly because you kill everything in the reservoir, expensive due to chlorine loss, subject to side effects (like this one), and ideally suited to breeding chlorine-resistant bacteria... not to mention giving you nigh-undrinkable water!

I'm from the UK, and we chlorinate our water pretty heavily, but even we don't do this.

(I now live in Switzerland. Water in Zürich is purified via activated carbon, live biofilm and ozonation. The water which comes out of the tap is unchlorinated and is better and more drinkable than most bottled mineral water.)

I think the story sounds a bit ironic:

So you are essentially dumping objects made out of chemicals, you had to drill wholes in the ocean ground to get, into a lake, because you found out that the chemicals you dumped into it earlier kill you when the sun shines on them. You also think that this might help you with the water shortage caused by unsustainable use of resources.

To me this all sounds like we arrived at a local maximum here. This simply cannot be the way to do this. Maybe we should start over.

Unless you have a better idea, I don't see how the criticism is useful.

I would stop trying to beat nature and instead try to play along with it. There is no need to waste that much water on farming in California. It is ridiculous to do this when you have a population density like the US has. There is just so much more suitable space all over the country.

But we protected ourselves from diseases with the chlorine. That's a massive win. Then we discovered there's a new risk of disease with the bromate, so we protect ourselves from that too. Isn't this basically how most technology develops? We keep getting better and better off because of it.

There are countries that don't use chlorine: Switzerland, Austria, Germany, Sweden, ... and they're regularly touted as having the best tap water quality in the world.

Ozone purification is cheap but could allow for future contamination if there is backflow or possibly a leak in the water mains. Chlorination prevents anything from growing in the water from the filtration plant to your home.

One problem that major coastal cities have is that they collect water from streams that have already been polluted and are on their way out to the ocean. The US has a lot of these cities, 40% of the population occupy the coasts which is only 10% of the country. The cities in the US that typically are regarded as having the best tap water are midwestern cities, ones that do not have a coastline and tend to get cleaner water from natural sources. Switzerland, Austria, and Germany are exactly the same. They are very central countries with nearby access to Alpine runoff water, the water they get is pretty unmolested when compared to what the Potomac River supplies to Washington DC.

I wouldn't be surprised if the balls increased the evaporation rate, for the simple reason that it will increase the surface area of the water (the balls will rotate in the water, bringing wet surfaces up). Black balls will also heat up more, causing more evaporation.

> Black balls will also heat up more, causing more evaporation.

Question. Overall, is the heat absorption of the black balls greater than open water? I imagine it's about the same, but perhaps the issue is that the balls are concentrating the heat at the surface, and on the surface of the rotating balls. So it does seem like the evaporation rate could well be higher.

I suppose it comes down to the mean rotation rate of the balls.

Smart thinking. The balls could be slightly weighted to avoid this issue, albeit this could mean the balls collect a rim of sludge more easily.

> the balls collect a rim of sludge more easily

Not sure if that's a massive issue, that would probably seal the water off even more effectively. That makes me think that this whole balls idea will limit gas exchange too, i.e. much reduced oxygen absorption, but I guess if they want no life in the reservoir that's not an issue.

Overall though I can't help feeling like there are going to be some significant unintended consequences with this scheme.

The weighting won't prevent them from sloshing around due to wave action and getting the upper surfaces wet anyway.

They'd be fine. For example, the tops of these ducks are dry:

https://i.imgur.com/RYyBMrf.jpg

In a reservoir you're not going to get waves that manage to spin the weighted side of the ball up any considerable amount, even if it's only slightly weighted.

Actually maybe I'm talking out of my behind -- what if there was wind? Add more weight then. Obviously a weighted oblate spheroid, like the ducks, would definitely work.

Not if the dye they are using to paint these balls is hydrophobic.

What I don't understand is that they dumped black balls in the reservoir. If you want to keep the water cool to lessen evaporation wouldn't it make sense to use white or reflecting balls so the water stays slightly cooler?

I would be glad to know why black balls are chosen.

black is best suitable color to deflect UV rays.

Now you just said the opposite of what intuition suggests without any evidence, or even argument. Please elaborate and don't just heat up the discussion!

Black is the best colour to absorb UV. You want the UV to not reach the water, so you want whatever is on top of the water to not allow UV past.

UV + Chlorine = Bromide

Does that look like an explanation to you? I don't see anything about black. I don't see anything about white. I don't see anything about reflecting materials. I see something from chemistry, maybe?

Customer: "Why should I buy the product?" Developer: "Here we had a problem with the inheritance tree. We worked around it with a factory method."

According to a chemist on /r/askscience, the plastics probably contain carbon black [0] as a UV protectant. So it might not be deliberate.

    (/u/Platypuskeeper) Although I have not seen a specification of what
    the balls are made of, what I know from polymer chemistry is that the
    black is quite likely from carbon black (essentially soot), which is
    used as an additive/filler in polymers (e.g. tire rubber) for multiple
    reasons but not least UV protection. Carbon black is one of the most
    (if not the most) effective UV-protective additives, precisely because
    it absorbs the UV and prevents it from penetrating deeply into the
    plastic. Plastic without some UV protective additive would degrade
    pretty quickly in the California sun, not least HDPE which has pretty
    bad UV resistance.

https://www.reddit.com/r/askscience/comments/3gpu6x/why_are_...

[0] https://en.wikipedia.org/wiki/Carbon_black

Black absorbs more light (and, yes, heat), which means less light penetrates through it to heat the water directly. If you block one bright light with a sheet of thin white plastic, and another with a sheet of thin black plastic, you'll see a lot more light shining through the former. And do remember that the primary purpose is to block UV, not heat, so you want maximum light absorption even if it means greater heat transfer.

Chrome-mirrored balls would certainly be even better, but the whole reason they're using plastic balls is because they're dirt cheap. If you have enough money to fill your reservoir with disco balls, you'd be better off just building a gigantic awning.

Thanks for making a bit of sense of this!

The primary purpose of these is not to slow down evaporation. In fact they have a negligible effect on the rate of evaporation.

Their primary purpose is to absorb the light spectra that drives chemical reactions in the treated water to prevent carcinogenic bromate from being formed.

Most of the reporting on this, including this article, is pretty bad, and causing a lot of laymen to ask questions like yours, because it doesn't make sense as described in the reporting.

Looks like 3d simulation example came to life :)

But seriously, why balls are used? They say it's cheap but 36 cents doesn't look too cheap on the hundreds of millions scale. Wouldn't it be better to use sheet-like form? It will be covering space more efficiently.

I wonder if floating solar PV was considered as an alternative/complementary solution that might pay for itself over time:

http://www.eastgreenenergy.co.uk/for-business/products/float...

Do they really need to invent that much? It's true that the current situation is maybe the worst they ever faced. But there are a lot of places where water is even more valuable as a resource. Are they also looking into what people in the desert do to keep their water sources alive, etc?

I do wonder if it's a different set of challenges. The demand for water in California is probably much greater, rather than adapting everyone's use to the climate. So I suspect the innovation is to sustain the level of water usage that isn't seen in the desert.

Hm, okay. I guess that's the American Way to approach such a problem.

This chlorine everywhere in the US astonishes me. When visiting I'm not able to drink (non bottled) Coke b/c of the bad and intense chlorine taste.

"in which a total of 96 million balls have been poured"

"they're cheap (costing just 36 cents per unit)"

Is that really cheap, or is it just because it's in LA?

Depends on the ball ... you need to use food grade plastic. And certifications and on and on and on ...

As sibling poster [1] mentioned, the balls are cheaper (and probably last longer) than the tarp alternative.

[1] https://news.ycombinator.com/item?id=10052777

Since it's LA, they could have recycled millions of silicon breast implants instead of using plastic balls. ;)

The article title is misleading. If we assume water price of $1000/acre-foot, then they spending ~$30m today to save 10x$2m over the next ten years. Water Davis are clearly a by-product benefit (as the article states) and the balls are not being used to tackle drought.

10 Year lifetime? Just the lifespan of these plastic balls being beaten with sunlight?

http://imgur.com/JagJndf

Reply on news.ycombinator.com