Traveler (Hydro)

5★

HydroSwordSupport

TL;DR

Hold the Skill and they spend six seconds spraying water wherever you point the camera. That is about the most controllable Hydro application in the game, which is why they end up in Bloom teams. It costs them health while they do it, and the water drops it leaves lying around give the health straight back. The Burst is a small bubble you cast when you have the Energy and otherwise ignore.

Rotation

Hold Skill (E), aim at the enemies and spray for the full six seconds.
Walk over the water drops it left around your feet to take the health back.
Burst (Q) if you have the Energy for it. If you do not, skip it.
Swap to your Dendro character and set off the Blooms.

Abilities

Skill (E)	Tap and it throws one wave forward. Hold and you go into aiming mode, firing a stream of droplets for up to 6 seconds, then the wave goes out at the end anyway. About a 10 second cooldown either way, so the hold is nearly free.
Burst (Q)	Costs 80 Energy, back in about 20 seconds. A slow floating bubble that damages enemies near it for about 4 seconds. That is not a typo, it really is four.
The water drops	Each droplet that hits an enemy leaves one of these on the ground near the Traveler, up to four a cast. Walk over one and you get 7% of their health back.

The one mechanic to understand

The hold mode pays in health.

While you are holding the Skill above half health, the droplets hit much harder and the Traveler bleeds a fixed slice of health every second. Below half it stops on both counts, so it cannot kill you and it will not keep draining forever. That is the trade, and the passive is built to soften it: every droplet that connects drops a water pickup near your feet, and walking over one hands back 7% health. So the loop is spray, then wander over your own puddles on the way out. Whatever health you did spend also gets added onto the wave that fires at the end of the hold, so none of it is wasted.

What actually matters

The two or three real decisions. Everything else is noise.

Hold, always. The tap version is one wave. The hold version is one wave plus six seconds of aimed Hydro plus four healing pickups, on the same cooldown. There is no situation where tapping is the plan.
Elemental Mastery in every slot. In a Bloom team nearly everything they contribute is reaction damage, and reaction damage reads off Elemental Mastery and cannot crit.
Aim on purpose. The whole reason to bring them over another Hydro character is that you decide which enemy gets wet and when. Point at the one your Dendro character is about to hit.

Gear

A build that works. KeqingMains lists every other option.

Weapon	Exaiphanes Blade, free from the Snezhnaya Archon Quest and the best sword on every Traveler form. No ascension materials, no mora, you level and refine it at that region's Statues of the Seven. Iron Sting is the craftable stand-in until then, since Elemental Mastery is the stat the rest of the build wants.
Artifacts	4-piece Gilded Dreams for the Elemental Mastery. 4-piece Instructor is worth a look while your Gilded Dreams pieces are rubbish, because the Elemental Mastery it hands the whole party after a reaction does not care that the pieces are only 4-star.
Main stats	Elemental Mastery sands, Elemental Mastery goblet, Elemental Mastery circlet. A Hydro damage goblet is a trap here, since the Blooms are where the numbers come from and they ignore it.

Works well with

Dendro

Electro

Dendro is the one that matters, since aimed Hydro into a Dendro aura is the job. Electro is there for the version where somebody else detonates the seeds.

Don't bother

Building around the Burst. 80 Energy for a four second bubble is not a rotation you want to plan on.
Crit substats. Reactions do not crit and that is nearly all of their output.
Panicking about the health drain. It stops at half and the pickups undo it.
Farming constellations any way but exploring. Hydro Traveler's come from levelling Fontaine's Statues of the Seven.

Want the full theorycrafting version? Read Traveler (Hydro) on KeqingMains.