But there is a cost…
The internet sleuths over at Reddit have found, fairly convincingly, a way to guarantee your preferred Eevee evolution (or “Eeveelution,” if you want to get cute about it). There is one obvious drawback and that is taking a hit to your Pokemon parentage autonomy and not naming all your Eevee “Vapelife” and praying to the vape gods for a Vaporeon.
I’ll let smithnigel explain,
It would seem that there is in fact a way to force an evolution of your Eevee. The Eevee Brothers from the original anime were named Rainer, Pyro, Sparky and they owned a Vaporeon, Flareon and Jolteon respectively. If you nickname your Eevee either Rainer, Pyro or Sparky, your Eevee will evolve into that desired Eeveelution!
Sparky = Jolteon
Rainer = Vaporeon
Pyro = Flareon
That is a deep cut and, apparently, it works. It makes some sense given how Pokemon Go, with its OG 151 (give or take a legendary) is trading on nostalgia not just for the original games, but the anime series as well.
Note that due to server issues, “it is recommended to name your Eevee with your intended evolution name, then close and restart the app to confirm the name went through on the servers.”