diff --git a/areas/maintenance/220_emerald.md b/areas/maintenance/220_emerald.md
index 6a76d3d..0bae86e 100644
--- a/areas/maintenance/220_emerald.md
+++ b/areas/maintenance/220_emerald.md
@@ -4,7 +4,6 @@ Type: Primary Residence
 ---
 
 # 🏠 220 Emerald Maintenance Log
-
 This document tracks maintenance and supplies for the home at 220 Emerald.
 
 ## 💧 Water Filtration System
@@ -19,9 +18,26 @@ This document tracks maintenance and supplies for the home at 220 Emerald.
     - 2026-04-26: Added 2 bags salt pellets; peroxide purchase pending.
     - 2026-04-25: Family noted this as the relevant date for the 90-day/3-month follow-up reminder.
 
-## 🚰 Drinking Water Filter
-- **Last Service:** (Pending)
-- **Check Cycle:** (Pending)
+## 🚰 Drinking Water Filter — 4 Stage Residential RO
+- **Discovered:** 2026-07-13 from manual photo (Page 11 of 12 - 4 STAGE USER MANUAL)
+- **Type:** 4 Stage Reverse Osmosis Drinking Water System (under kitchen sink)
+- **Flow:** Cold water → Angle Stop Adaptor (HDFS-ASVA-14) → Sediment (SOC-25-1005) → Carbon Block (CB-25-1005) → Automatic Shut-off Valve (ASV-14QW) → Membrane Housing (MH03-1812WH) with Flow Restrictor FR-550QC → Post Carbon ICF-10Q → Tank RO-4S-W14 (4.5 gal white) + RO Faucet LF-LR-5TND → To Faucet / To Drain via Saddle DS-14QC
+- **Manual Photo:** `attachments/ro_system_manual_page11_2026-07-13.jpg`
+- **Replacement Cycle:**
+  - Stage 1 Sediment + Stage 2 Carbon Block: every 6-12 months
+  - Stage 4 Post Carbon (ICF-10Q): every 12 months / 2000 gal
+  - Stage 3 Membrane 50 GPD (TW-1812-50): every 2-3 years
+- **Last Service:** (Pending - unknown, log when replaced)
+- **Next Check Due:** ASAP - check last change date, overdue if >12 months on Stage 1+2
+- **Filters to Buy (exact part numbers from manual):**
+  - Stage 1: `SOC-25-1005` — Hydronix NSF Sediment Filter 2.5" X 9.75" 5 micron — QTY 1
+  - Stage 2: `CB-25-1005` — Hydronix NSF Carbon Block Filter 2.5" X 9.75" 5 micron — QTY 1
+  - Stage 3: `TW-1812-50` — Hydronix NSF TFC 50 GPD Membrane Dry — QTY 1 (upgrade option: TW-1812-75 = 75 GPD, same housing)
+  - Stage 4: `ICF-10Q` — Hydronix Inline Coconut Filter 2000 Gal, 2" x 10", 1/4" Quick Connect — QTY 1
+- **Kit Search:** `SOC-25-1005 CB-25-1005 ICF-10Q TW-1812-50` — 4-pack kit ~$45-65 on Amazon
+- **Compatible Generic Spec:** 2.5"x9.75" 5mic sediment + 2.5"x9.75" 5mic carbon block + 2"x10" inline post QC + 1812-50 membrane
+- **Hardware (do NOT replace routinely):**
+  - `HF2-10WHWH14` Housing 10" white 1/4" QTY 2, `RO-4S-W14` Tank 4.5G, `LF-LR-5TND` Faucet chrome, `DS-14QC` Drain saddle, `ASV-14QW` Auto shut-off, `FM-60W` Bracket triple, `CLP-25W` Clip 2.5" QTY 2, `CLP-2520W` Double clip QTY 2, `MH03-1812WH` Membrane Housing, `FR-550QC` Flow restrictor 550ml/min 90gpd, `HDFS-ASVA-14` Angle stop adaptor, `HDF-ASVA-14` Tube elbow, `HDF-FE0602` Elbow QTY 2, `HDF-FE0404` Check valve, `HDF-BVTD0404` Tank ball valve
 
 ## 🔥 Boiler Filter
 - **Last Service:** (Pending)
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