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Comment by tristanj | Hacker News Reader

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...

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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.

> 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."

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

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