Borderlands 4: The Tainted Truth Full Quest Walkthrough

The Tainted Truth is a hard-difficulty side mission on Providence Island, the map added with the FL4K and the Last Resort story pack. It starts with a conspiracy theory about the local water supply and ends with you rebooting an entire purification plant after killing the Tediore officer squatting inside it.

Quick answer: Talk to Joanie in the Bagheera Range, drive to the Bilge Purification Plant, blow open the wall with Oscar’s explosives from the dumpster, clear the basement and restart the water flow, destroy the five digilament tanks upstairs, open the reservoir hatches and shoot the gunk out of the pipes, then kill Lieutenant Bume and use the main console to restart the plant.

The Tainted Truth mission details and rewards

Detail	Value
Type	DLC side mission (hard difficulty)
Mission giver	Joanie
Start location	Bagheera Range, Providence Island
Objective area	Bilge Purification Plant
Boss	Lieutenant Bume
Rewards	Fully Loaded MIRV Reaver legendary grenade mod, Deep Dive ECHO-4 attachment

If the blue exclamation mark for Joanie is missing from your map, push further into the story pack’s main quests. Providence Island side missions unlock as the DLC campaign progresses, and unfogging the Bagheera Range makes the marker appear.

Start the mission and reach the Bilge Purification Plant

Find Joanie at her marked spot in the Bagheera Range and accept the mission. She spends the intro explaining why she thinks the island’s water is being poisoned, and the objective updates once the conversation ends.

Call in a Cyclone and drive across the Bagheera Range to the purification centre. It is a long ride, so the vehicle saves several minutes over sprinting.

Aiming down the path through the Bagheera Range on the way to the purification plant — Crossing the Bagheera Range toward the plant after taking the mission from Joanie. Image: Gearbox Software

Fight through the Tediore forces at the plant entrance. Lieutenant Bume taunts you over the intercom as the first waves spawn, and the group mixes Radioactive TedMechs, Incendiary and Energized Troubleshooters, Adjutants, Energized Demolitionists and Toxic Frames.

Get inside: the dumpster, Oscar, and the wall weak spot

The front door stays locked, so the mission routes you around the side of the building instead.

Follow Joanie’s direction to the refuse pile on the side of the plant. Drop down to the lower ledge and open the dumpster there.

Looking over the exposed pipework and basin at the Bilge Purification Plant — The exterior pipework and basin at the Bilge Purification Plant, next to the refuse area you search for a way in. Image: Gearbox Software

Talk to Oscar, who is living in the dumpster, and take the homemade explosives he hands over. This replaces the lockpick Joanie originally sent you to find.

Climb back up to the marked weak spot on the exterior wall, clearing the enemies that spawn on the way. Place the explosives, back off, and detonate them to open the breach.

Clear the basement and restore the water flow

Head through the breach into the basement and wipe out the Creeps nesting there. Expect Tropical Sunbeam Creeps, Tropical Peashooter Creeps and Caustic Honeycomb Creeps, so an element that handles armour and flesh mixes works best here.

The Clear out the basement objective highlighted on screen inside the plant — The objective tracker switches to clearing the basement once you are inside the plant. Image: Gearbox Software

Interact with the consoles down there to turn the water flow back on. The objective completes as soon as the last switch is thrown.

Step into the water spout that erupts in the middle of the room. It launches you up to the plant’s upper level, which is the only way forward.

Destroy the five digilament tanks and unclog the pipes

The upper floor is where Joanie’s theory is confirmed. The tanks are full of ground-up Tediore guns being fed straight into the island’s water.

Track down and destroy all five digilament tanks. They are spread around the upper walkways and each one is marked, so sweep the level rather than staying in one spot.

Use the control console to open the reservoir hatches. This exposes the blocked pipe sections.

Shoot the blue gunk sitting in the pipes until both blockages clear. The counter on the objective panel ticks up as each one breaks apart.

Unclog the pipes objective at 0 of 2 while aiming at a marked pipe section — The unclog the pipes objective tracks two blockages, both cleared by shooting the blue gunk. Image: Gearbox Software

Beat Lieutenant Bume and restart the plant

Hold the area against the large Tediore wave that drops in once the pipes are clear. This is the heaviest fight of the mission, so use the walkways and cover rather than standing in the open.

Kill Lieutenant Bume when he finally commits to the fight. He is a badass-tier officer with adds trickling in around him, so clearing the smaller enemies first keeps the damage manageable.

Walk to the main console and restart the water plant. The mission completes at that interaction, with Joanie confirming the water supply is running again over ECHO.

Rewards: Fully Loaded MIRV Reaver and Deep Dive

Completion pays out two items. The Fully Loaded MIRV Reaver is a legendary grenade mod, and Deep Dive is an ECHO-4 attachment. Both land in your inventory rather than on the ground, so open the menu after the plant restarts to equip them.

Fully Loaded MIRV Reaver grenade mod highlighted on the mission rewards screen — The Fully Loaded MIRV Reaver grenade mod on the rewards screen after the plant is restarted. Image: Gearbox Software

Note: if the mission does not tick over as complete, check that all five digilament tanks are destroyed and both pipes are clear. Those two counters are the usual reason the console interaction stays greyed out.

The Bagheera Range holds two more side missions once you are done here, Pay to Play and The Rusty Butler at the Ol’ Abandoned Resort, so it is worth clearing the region in one trip while you already have a Cyclone parked outside the plant.