They said the same about milk years ago when farmers would add water to get a higher yield. Now there are analysis methods to check the water content, and if it's too high the batch gets rejected and you can be fined.
I don't know if the same system can be used for alcohol since it has a much lower freezing point but it can be analysed.
There should be no added water in milk, unless it's marketed as milk (a milk by-product) that's been made from the condensed milk or the milk powder.
When it comes to beer, my understanding is that the regulation only specifies the contents, not the recipe or how it should be made (the sequence of the production process; sure, there are product safety guidelines, but that's not it).
And as the defence, has already said:
Our beers are in full compliance with all alcohol labeling laws
So, if you look at the label of a beer bottle, under the ingredients it will say: water, malted barley, hops.
The judge will throw away this case as soon as the process starts. There's no substance. And not one consumer has been duped.