All right...I searched for this topic and couldn't find anything discussing this exact topic.
I'm a relatively new brewer (<2 years) who brews on an apartment sized electric stove with no option for outdoor brewing. I've tried doing AG with 2 pots but the ****ty stove can't keep anymore than 4 gallons rolling even if its in 2 pots. So here's my new plan: I buy enough grain for a 2X the original gravity half batch and then dilute with pre boiled tap water to hit the original gravity. With my crappy 23L plastic bucket false bottom mash ton, my efficiency is abysmal but it is still considerably cheaper than extract brewing. And with the reduced volume, there is virtually no sparging needed to fill the boil kettle so it doesn't take anymore time than an extract/specialty grain batch. Aside from the waste of grain (which is cheap) and the extra hops needed due to the high gravity boil (same problem as extract partial boil brewing) it seems like a good method. It seems better, cheaper and easier than doing partial mashes (I always had acidity problems due to the high ratio of roasted grains:base malt). The only downside that I see that can't be rationalized away is the limited OG - its hard to hit anything more than 1.050 on a 19L batch. I have done a couple batches like this and they turned out well. Has anyone else done it this way? How come this isn't a more popular method? I'm currently using Beer Alchemy (I'm a mac user) to sort out the recipes and its worked well but the colour hasn't come out as expected. Maybe it would be better to steep the specialty grains separately?