Blue-only puzzle (no green needed) — sprawling layout, heavy loot, no scientists.
Mid-game puzzle monuments. Most need a green card → blue card progression and one fuse. Loot tier rises sharply (military crates, elite crates, components, scrap) — the meat of the monument economy.
| Keycards | 1× Blue |
|---|---|
| Fuses required | 1 |
| Scientists / NPCs | 0 |
| Radiation | None |
| Recycler | Yes (×2) |
| Workbench | Tier 1 |
Water Treatment Plant is unique among the Tier 2 puzzle monuments — it's the only puzzle that needs just a blue keycard (no green-card prerequisite). One blue card, one fuse, no scientist defenders, no radiation. Sprawling industrial layout with two recyclers, multi-storey loot rooms, and the cleanest loot-to-risk ratio in the blue tier.
The puzzle is simpler than Airfield's despite the larger monument footprint:
Water Treatment's footprint is larger than most monuments — give yourself 8-10 minutes for a full clean sweep:
A single blue keycard plus one electrical fuse — uniquely, no green keycard is required despite this being a Tier 2 monument.
No — Water Treatment has no NPC defenders. The whole monument is purely keycard-and-fuse based with no combat risk from PvE.
No — Water Treatment is rad-free. Standard clothing is fine.
One of the largest monument footprints in the game — give yourself 8-10 minutes for a thorough sweep across the multiple buildings, cooling towers and pipe sections.
Excellent for solos — no scientists, no radiation, and the only Tier 2 monument that doesn't require a green card. The puzzle layout itself is also straightforward.
Water Treatment Plant breaks the standard Tier 2 progression. Where Airfield, Trainyard and Power Plant all need a green card → blue card chain, Water Treatment skips the green card entirely. This makes it the easiest Tier 2 to access if you've already got a blue card from another source — usually a previous Trainyard or Airfield run, or a lucky barrel drop.
The combat-free design also makes it the safest Tier 2 for solos. No scientist defenders means the only threat is other players, and the sprawling layout gives multiple cover positions for fighting back. New players doing their first Tier 2 monument should consider Water Treatment first — the puzzle pattern is the same as Airfield's, but without the scientist combat overhead.
The trade-off for the no-PvE design is that loot-per-second is lower than Airfield. The puzzle-room rewards are similar, but Airfield's density (everything in two hangars) makes it faster to clear. Water Treatment's spread-out layout means a thorough sweep takes 8-10 minutes versus Airfield's 4-6.
For your full Tier 2 route, see the Monuments hub. For raid math, the Raid Calculator covers explosive cost vs target HP.