Step 1: Identify the source
Water at the toilet base can come from four different leak points. Diagnose before repairing — fixing the wrong one is wasted work.
1. Dry the entire toilet and floor thoroughly with a towel. Sprinkle baby powder or food coloring around the base. Wait 30 minutes without flushing.
- If powder is wet around the base before any flush: condensation or supply-line leak
- If water appears only after flushing: wax ring failure
- If water appears under the tank (not base): tank-bowl gasket (two-piece only)
- If water trickles down the side of the tank: supply-line connection or angle-stop drip
Fix 1: Wax ring failure
Most common cause. Symptoms: water emerges from under the porcelain base only when flushed. Fix: pull the toilet, replace the wax ring (see our dedicated wax-ring guide). 60-minute DIY, $5-10 in parts.
Fix 2: Tank-bowl gasket (two-piece toilets only)
Symptoms: water drips from where the tank meets the bowl, runs down the back of the bowl onto the floor — usually only during/right after a flush. Fix: shut off water, drain tank, remove the two tank bolts at the base, lift the tank off, replace the spud gasket (the large rubber donut between tank and bowl). New gasket ~$10, takes 30 minutes. The bolts and rubber washers should be replaced at the same time.
Fix 3: Supply-line connection
Symptoms: water at the angle stop, supply line, or where the supply enters the tank. Often slow-drip continuous (not flush-related). Fix: shut off angle stop, replace the braided stainless supply line ($8) and the angle stop itself if old/corroded ($12). 20-minute repair.
Fix 4: Condensation ("tank sweating")
Symptoms: water rolls down the outside of the porcelain tank, drips off the bottom, pools at the base. Worst in humid summer months or in basement bathrooms. The cold tank water cools the porcelain below the dew point of room air, causing condensation. Fix options: (1) install an anti-sweat valve that mixes warm water into the tank fill ($30 valve + 30-min install), (2) install a foam tank liner (cheap but lasts 3-5 years before mildewing), (3) better bathroom ventilation, (4) accept it and place an absorbent mat at the base.
The "ghost" leak
If you\'ve replaced wax ring and gasket and water still appears: check the floor flooring/subfloor itself. A long-running prior leak may have rotted the subfloor — water now wicks through rotted wood and emerges away from the actual leak point. Probe the subfloor around the flange with an awl. Soft wood means subfloor replacement before another toilet can be installed.
When to call a plumber
If the leak persists after replacing the wax ring, tank-bowl gasket, and supply line, or if you find evidence of subfloor rot or flange damage that you don\'t feel equipped to repair, call a licensed plumber. Long-running base leaks cause ceiling damage, joist rot, and (if the toilet sits over a bathroom) mold colonization in the floor cavity.