my aquasana under sink filter is dripping water from the housing, not the connections, just a slow drip from the plastic itself.

Diagnosis

The slow drip emanating directly from the plastic body of the Aquasana AQ-5200 housing is almost always indicative of a stress fracture or a hairline crack in the polypropylene sump. Unlike a leak at the connection point (which is usually a faulty O-ring or loose fitting), a leak through the plastic itself means the structural integrity of the vessel has been compromised. This typically occurs due to "over-torquing" the housing during a filter cartridge replacement, where the pressure of the wrench creates micro-fractures in the plastic that only open up under the constant 40-60 PSI of household water pressure. In some cases, this is caused by "water hammer" (pressure surges) or thermal shock if the system is installed too close to a hot water line, causing the plastic to expand and contract until it fails. You can confirm this by drying the housing completely with a microfiber cloth and using a bright flashlight to look for a "spiderweb" pattern or a singular vertical line where the water is seeping through. If you see water beads forming on the side of the plastic rather than dripping from the top rim, the housing is physically breached.

How to Fix It

Because polypropylene is a non-porous, chemically resistant plastic, you cannot "patch" or glue a cracked housing; the pressure will simply blow the patch out. The only permanent solution is a full replacement of the housing sump.

1. Shut off the cold water supply valve leading to the AQ-5200 system. Open the dedicated faucet to bleed off all remaining pressure and water trapped in the line.
2. Using the provided Aquasana plastic filter wrench, rotate the cracked housing counter-clockwise to unscrew it from the head assembly. Be prepared for a rush of water as the seal breaks.
3. Remove the spent filter cartridge and inspect the head assembly (the top part) for any corresponding cracks. If the head is intact, proceed.
4. Acquire a replacement housing sump (Part Number 304010-59). Ensure the replacement is the 3/4" standard size compatible with the AQ-5200 series.
5. Clean the O-ring located at the top of the housing. Apply a thin layer of food-grade silicone lubricant to the O-ring to ensure a watertight seal and prevent the rubber from pinching.
6. Insert the new filter cartridge into the new housing.
7. Screw the housing back into the head by hand until it is finger-tight.
8. Use the filter wrench to tighten the housing an additional 1/4 turn. Do not over-tighten; the seal comes from the O-ring compression, not the force of the plastic threads.
9. Slowly open the water supply valve and check for leaks for 5 minutes before putting the system back into full use.

If That Didn't Work

• Check the Head Assembly for Hairline Cracks: If the new sump is installed correctly but the drip persists, the crack may actually be in the head assembly (the stationary top part). Inspect the threads and the plastic "shoulders" of the head. If the head is cracked, the entire unit must be replaced as the head cannot be swapped individually without risking a catastrophic burst.
• Inspect the O-Ring for Nicks: A "leak from the plastic" can sometimes be a deceptive O-ring failure where water travels down the exterior side of the housing, making it look like the plastic is leaking. Replace the O-ring with a genuine Aquasana replacement part and ensure there are no grains of sand or debris on the sealing surface.
• Install a Pressure Regulating Valve (PRV): If you have experienced multiple housing failures, your home's static water pressure may be exceeding 80 PSI. Install a PRV on the main line to bring the pressure down to 50-60 PSI to prevent future stress fractures in the polypropylene.
• Verify the Cartridge Seating: Ensure the filter cartridge is centered perfectly within the sump. If the cartridge is tilted, it can put uneven pressure on the housing walls during the tightening process, leading to localized stress points.

Heads Up

• Never use Teflon tape on the plastic threads of the housing; the system relies on the O-ring for the seal, and tape can actually prevent the housing from seating deeply enough to engage the gasket.
• Always use the specific Aquasana wrench provided. Using a pipe wrench or pliers will mar the plastic and create the very stress fractures that lead to leaks.
• Replace your O-rings every 12 months or whenever you notice a decrease in water pressure, as dried-out rubber can lead to "creep" leaks.
• Avoid installing the system in areas subject to extreme temperature swings (like uninsulated cabinets against exterior walls), as this accelerates plastic fatigue.