Material
The most-used tool in the craft, and the one nobody thinks to list among their tools.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
Wherever there is a threshold rite there is water. Wells and springs named, visited and left offerings at; rag trees beside them; rivers treated as boundaries in a legal sense and a magical one at once. Frazer collected water customs across Britain, Ireland and Europe in bulk, and the striking thing is how little instruction anyone needed — water for washing something off is not a doctrine, it is a habit with a long reach.
Practitioners distinguish waters by where they came from: rain, spring, river, sea, snowmelt, dew, and, honestly, the tap. Whether the source changes anything is exactly the question the craft does not answer. That it changes something for the practitioner is easy enough to verify, and is probably how the distinction started.
Keep it sensibly. Collected water is not drinking water; standing water grows things within days; rainwater carries whatever was on the roof, and sea water will corrode anything metal it is stored near. Label jars, keep them out of the kitchen, and throw them out when they turn.
Readings practitioners have offered, ordered by how many recognise them. Take what serves, leave the rest.
Carried forward
James Frazer, The Golden Bough (1890)
Frazer describes the rags tied at holy wells across Britain and Ireland — the cloth touched to the trouble, then left on the tree, the ailment expected to go as the rag rots. He points out that the logic requires the rag to be abandoned rather than retrieved, which most people found the hardest part.
Carried forward
Common in contemporary practice
Water from a place the practitioner actually walked to, rather than a bottled label. The reasoning offered is that the journey is doing at least as much work as the water.
Credit what you carry. Much of this comes from living traditions, and some of it from traditions that are closed — held by particular peoples and not offered for general use. Where you know whose practice a reading came from, name them; where you don't, say that too.