Overshot OG - How To Dilute

So I'm trying to make a pale ale that is around 4.7% ABV but unfortunately (or fortunately) my mash was far more efficient than usual meaning my OG wasn't 1.040 but was 1.059.

I've read a bit about blending water post fermentation in order to dilute a strong beer and get more from a batch like commercial breweries do.

Can anyone shed any light on this, tips, etc?

Thanks.

Also, would be interested to know whether anyone has added water during fermentation and what effect this had.

I've done it. I just used bottled distilled water. I added it in right before I pitched my yeast. It will also dilute your IBUs too. Beersmith has a tool you can use to figure out how much to add. If this is a 5 gallon batch, you probably have to add over 2 gallons to get it down to 1.040. I don't know if I'd add that much, but its up to you.

I add a quarter gallon of water (tap) at a time, shake the fermenter for about 30 seconds, then take another hydrometer reading. Repeat until you get the desired OG. This has always worked well for me. I have not tried adding water after pitching yeast.

I've done it two ways, before pitching and before bottling. Both work. As above, you can use a calculator or do the math.
1.040 seems a bit low to get to 4.7%. Are you sure that's right?

Brewersfriend seemed to suggest that the OG should be 1.040 and FG 1.007. I probably need to readdress the math as something evidently is wrong somewhere.

That aside, would the beer take much harm if I added water during fermentation? It was only after pitching the yeast and went to bed that I thought about diluting it, or should I wait until bottling now?

Are you sure your measurement is correct. Seems like a big error more likely due at least in part to measurement error.

What was the grain bill (simple total weight is all that's needed), projected efficiency and volume to FV.

If the measure is correct, volume is known the adjustment is easy enough.

If the volume collected is 5.5 gallons at 1.059, 2.6 gallons of water needs to be added to bring it down to 1.040. FV space will be an issue. Probably not feasible.

Adding 1 gallon will dilute it to 1.050. More realistic.

Edit a 4.7%ABV beer will usually be about 1.047 to 1.050 assuming attenuation is in the 75-80% range. Very rough figures but an indication something is a miss in calculations or measures or both.

I did water addition from bottle water before pitching, after pitching, at the end of the primary fermentation, during the priming (boiling sugar in one liter of water). I also tried to keg a 'light' version of the beer, diluting with 10% water the beer that has been putted in the keg, and I saw hardly any dfference from the bottle version (undiluted)

But in all those cases it was maximum 15% of the total volume.
In your case you will need to add the 25% of te batch volume in water. What about the IBU? did you stay 25% higher than expected? otherwire you'll have a less bitter beer

I added 4 litres of boiled then chilled water yesterday to the fermentor. Could possibly get another 1L in but am going to leave it as it is.

My grain bill was 5.05KG Maris Otter and 200g torrified wheat. I'm doing BIAB so that went in 29.5L water. My efficiency is usually around 70%. I worked all the math out on Brewer's Friend but I must has put a miscalculation in somewhere.

When i did it with Beer Smith it was more accurate to what I actually turned out with (1.059 OG).

My bitterness is 25IBU. I appreciate that it won't be as bitter diluting the beer but it's meant to be quite a smooth drinking English pale ale. The last time I made it, I diluted a strong wort (but it was partial mash) and hadn't taken then IBU into consideration, but the beer turned out great.

Hopefully this will yield the same results.

Good. Let us know how it turns out. Coincidentally, I have an ESB in the fermenter right now that also came out too strong. It stopped bubbling overnight, I plan to add a gallon of bottled water to it soon.