diff --git a/server/src/systems/__tests__/systems.test.ts b/server/src/systems/__tests__/systems.test.ts
index b8b2cfc..65652c3 100644
--- a/server/src/systems/__tests__/systems.test.ts
+++ b/server/src/systems/__tests__/systems.test.ts
@@ -1,4 +1,4 @@
-import { describe, it, expect } from 'vitest';
+import { describe, it, expect, vi } from 'vitest';
 import { World } from '../../ecs/World.js';
 import { GameMap } from '../../map/GameMap.js';
 import { needsDecaySystem } from '../needsDecaySystem.js';
@@ -13,7 +13,7 @@ const rc = createRuntimeConstants();
 function createNPC(world: World, x: number, y: number, hunger = 80, energy = 80) {
   const e = world.createEntity();
   world.addComponent<Position>(e, 'position', { x, y });
-  world.addComponent<Needs>(e, 'needs', { hunger, energy, productivity: 80 });
+  world.addComponent<Needs>(e, 'needs', { hunger, energy, thirst: 80, productivity: 80 });
   world.addComponent<Movement>(e, 'movement', { state: 'idle', target: null, path: [], direction: 0, moveProgress: 0 });
   world.addComponent<NPCBrain>(e, 'npcBrain', { currentGoal: null, goalQueue: [] });
   return e;
@@ -139,6 +139,36 @@ describe('needsDecaySystem', () => {
     const needs = world.getComponent<Needs>(e, 'needs')!;
     expect(needs.energy).toBe(100);
   });
+
+  it('decays thirst each tick', () => {
+    const world = new World();
+    const e = createNPC(world, 0, 0, 50, 50);
+    const needs = world.getComponent<Needs>(e, 'needs')!;
+    needs.thirst = 50;
+    needsDecaySystem(world, undefined, rc);
+    expect(needs.thirst).toBeCloseTo(50 - rc.get('THIRST_DECAY_PER_TICK'));
+  });
+
+  it('decays thirst at half rate during sleep', () => {
+    const world = new World();
+    const e = createNPC(world, 0, 0, 50, 50);
+    const needs = world.getComponent<Needs>(e, 'needs')!;
+    needs.thirst = 50;
+    const brain = world.getComponent<NPCBrain>(e, 'npcBrain')!;
+    brain.currentGoal = 'sleep';
+    needsDecaySystem(world, undefined, rc);
+    expect(needs.thirst).toBeCloseTo(50 - rc.get('THIRST_DECAY_PER_TICK') * rc.get('SLEEP_HUNGER_DECAY_MULTIPLIER'));
+  });
+
+  it('fires thirst crisis event when crossing threshold', () => {
+    const world = new World();
+    const e = createNPC(world, 0, 0, 50, 50);
+    const needs = world.getComponent<Needs>(e, 'needs')!;
+    needs.thirst = rc.get('THIRST_THRESHOLD') + 0.01;
+    const mockEMS = { record: vi.fn() };
+    needsDecaySystem(world, mockEMS as any, rc);
+    expect(mockEMS.record).toHaveBeenCalledWith(e, expect.objectContaining({ type: 'need_crisis', need: 'thirst' }));
+  });
 });
 
 describe('npcBrainSystem', () => {
diff --git a/server/src/systems/needsDecaySystem.ts b/server/src/systems/needsDecaySystem.ts
index 6c86e6b..68e07a3 100644
--- a/server/src/systems/needsDecaySystem.ts
+++ b/server/src/systems/needsDecaySystem.ts
@@ -10,6 +10,7 @@ export function needsDecaySystem(world: World, eventMemoryService: EventMemorySe
     const con = getEffectiveStat(world, entity, 'constitution');
     const conMultiplier = 1 - (con - 10) * 0.03;
     const prevHunger = needs.hunger;
+    const prevThirst = needs.thirst;
     const prevEnergy = needs.energy;
     const prevProductivity = needs.productivity;
 
@@ -19,9 +20,11 @@ export function needsDecaySystem(world: World, eventMemoryService: EventMemorySe
     if (isSleeping) {
       needs.energy = Math.min(100, needs.energy + rc.get('SLEEP_ENERGY_RECOVERY_PER_TICK'));
       needs.hunger = Math.max(0, needs.hunger - rc.get('HUNGER_DECAY_PER_TICK') * conMultiplier * rc.get('SLEEP_HUNGER_DECAY_MULTIPLIER'));
+      needs.thirst = Math.max(0, needs.thirst - rc.get('THIRST_DECAY_PER_TICK') * conMultiplier * rc.get('SLEEP_HUNGER_DECAY_MULTIPLIER'));
     } else {
       needs.energy = Math.max(0, needs.energy - rc.get('ENERGY_DECAY_PER_TICK') * conMultiplier);
       needs.hunger = Math.max(0, needs.hunger - rc.get('HUNGER_DECAY_PER_TICK') * conMultiplier);
+      needs.thirst = Math.max(0, needs.thirst - rc.get('THIRST_DECAY_PER_TICK') * conMultiplier);
     }
     needs.productivity = Math.max(0, needs.productivity - rc.get('PRODUCTIVITY_DECAY_PER_TICK'));
 
@@ -44,6 +47,15 @@ export function needsDecaySystem(world: World, eventMemoryService: EventMemorySe
           detail: `${name} became exhausted`,
         });
       }
+      if (prevThirst >= rc.get('THIRST_THRESHOLD') && needs.thirst < rc.get('THIRST_THRESHOLD')) {
+        const name = world.getComponent<string>(entity, 'name') ?? 'Unknown';
+        eventMemoryService.record(entity, {
+          type: 'need_crisis',
+          tick: 0,
+          need: 'thirst',
+          detail: `${name} is getting dehydrated`,
+        });
+      }
       if (prevProductivity >= rc.get('PRODUCTIVITY_THRESHOLD') && needs.productivity < rc.get('PRODUCTIVITY_THRESHOLD')) {
         const name = world.getComponent<string>(entity, 'name') ?? 'Unknown';
         eventMemoryService.record(entity, {