From the article..
So you're still looking at a 2:1 waste water ratio. Although I guess you don't have to fill it from the tap you could use any water source.
Let's think about a gallon per square meter. Let's say we need 4 gallons per day, that's a decent sized tank between top-off and weekly water changes. So we need 4 square meters of solar still, if we achieve the output of the one mentioned. To put that into terms Americans understand, that is about 6'6" by 6'6". And then what do you do one day when you need more water? Say a coral slimes out and you need to do a few rapid water changes.
I don't know, it would depend on the source of the water. I only mention it because there seems to be this idea (especially around RC) that any time you evaporate and condense water that makes it distilled. People try to call the condensate off their airconditioner or dehumidifier the same thing as distilled. That just isn't the case. I only mention it to illustrate the point that if there were something there you're not going to get it out.
Rainwater can have a lot of nasties in it. First of all, every raindrop has at its core a speck of dust. But moreover, rain picks up a ton of dissolved gasses from the air. The CO2 isn't so big of a deal because all it does is drop the pH. But the other constituents of "acid rain" are soemtimes things you don't want in your tank. All the NOx species will become nitrate eventually. The SOx species will become sulfate, maybe not as big of a problem as nitrate but still.
And even this is assuming the rain came from a perfectly clean sky. Our air is rather polluted these days. With all the industry going on, there's a lot of stuff going up into the sky that comes back down with the rain.
The moral of that story is that rainwater isn't nearly as clean as you would like to think it is. Again, simply having evaporated and condensed does not make it distilled water.