Dark Souls Estus Flasks are nothing short of a lifeline, allowing you to replenish health between bonfires.
Of course, there are only so many refills available, but it's possible to increase the potency of your collection.
How to strengthen Estus Flasks in Dark Souls
In order to improve the strength of your Estus Flask, you will need to get a Fire Keeper Soul and hand it to a firekeeper in Firelink, Anor Londo or Quelaag's Domain.
Fire Keeper Souls can only be attained after killing a few Fire Keepers and allowing Lautrec to kill the Firekeeper in Firelink Shrine - it comes at a high cost and isn't an easy pill to swallow. They can be upgraded to a maximum of +7.
But that's not all. After managing to get your Estus to +7 - which is the maximum amount whether you're in your first playthrough or hitting NG+ - you may find that 5 Estus Flasks are simply not enough.
At most Bonfires, except for Firelink Shrine and Anor Londo, you'll only have five Flasks when you rest. However, there is a way to strengthen these bonfires and get a maximum of 20 at any certain Bonfire.
There is, of course, a caveat. Having attained the Rite of Kindling, you will need to then revert to your Human Form at the bonfire, and then only after this will you need to have 'Soft Humanity' to further kindle any bonfire up to three levels.
The first level upgrade will give you 10 Estus Flasks from that Bonfire, the second level will give you 15, and the third level will give you 20. Pretty nifty if you are finding yourself struggling against bosses or are going through a particularly tough area.
We recommend trying to get the Rite of Kindling early on before or after you complete Sen's Fortress - you may need the extra Flasks from kindling those Bonfires later on.
If you're looking for more help, our Dark Souls walkthrough and guide can help with all other areas of the game, including the dreaded Taurus Demon, Capra Demon, Ornstein and Smough bosses. Meanwhile, we have explainers on how to access DLC Artorias of the Abyss, the best gift and best class in Dark Souls, Dark Souls' best weapons, Dark Souls Covenants, Dark Souls Estus Flasks locations, Dark Souls Titanite Slab locations and NPC quests including Lautrec of Carim.
Estus Flask locations
The following are in the approximate order you'll find them in the game, and allow you to increase the number of Estus Flasks in your inventory.
In the hall of the Parish, you will find a Berenike Knight guarding a Firekeeper Soul that lies on a corpse.
New Londo Ruins:
This is an easy one to get, and can be attained early on in the game, where you will be able to grab it past the wooden walkway as you enter and in a building to the right along a small walkway guarded by ghosts- remember to bring your Transient Curses for this one.
From the second bonfire, head up the elevator and up a ladder, then, cross the narrow wooden bridge and you'll see a ladder heading down. There, you will want to head down, attacking the two Fire Dogs, and the Fire Keeper Soul is inside a cell on a corpse.
Dropped after killing The Fair Lady (Queelaag's Sister).
If you follow Lautrec's storyline, you will be able to get it after invading and killing him in Anor Londo.
Dropped after killing Lady of the Darkling.
Ensure you have the Archive Tower Giant Cell Key, in the room where Logan was, you will find a Soul on a corpse.