Probably because you have an Explorer's Ring. When you runecraft with an Explorer's Ring on, it "sparkles to life" and makes a few more runes for you. If you don't have one of these, I don't know why your number varies, but I do recommend that you get one. They come in handy a LOT. :D
Make runes. Air, Water,...
crafting runes at alters. Use runes ess at certain alter to craft those runes. Eg water alter you crft water runes.
You can make them with runecrafting, Buy them at the Grand Exchange, General Store, NPC Rune store, or Buy them from another player. I hope this helped, Peace, lolz
Crafting Water Runes.
At the Fist of Guthix. The runecrafting gloves cost 75 fist of guthix tokens each. You can buy Air, water, or earth runecrafting gloves there. Each set of gloves have 100 charges.
Water tiaras are used for quicker entrance into the water temple. Which is convenient compared to a water talismen. They are used for RuneCrafting.
go to every mage and fishing shop every day and buy all the water runes and earth runes and fethers
You can make the at the water altar, buy them from a rune shop, or buy them from the Grand Exchange.
Basilisks drops a lot of water runes on a regular basis, or you can buy them st a shop oor off a player or on GE, or you can simply make them yourself.
3 Water, 2 Earth and 1 mind rune
That depends what you want to do with it. In the simplest case, to make water runes, the water tiara will simply allow you access to the water altar.
Answer: Because to use magic on Runescape, you have to use runes, magical stones like air, fire, earth, water, mind, ext. Answer: And the "scape" is probably derived from "landscape".