It could be backpressure, which would mean the faucet's only made to fully retain water in one direction. Turn the faucet handle down until the faucet stops leaking. This is the maximum that the filter can handle or process.
On modern faucets, most leaky handles are caused by a worn faucet cartridge. On older faucets, the leak is usually caused by a worn washer or O-ring. You can bring...
You might luck out that way, but it's best to take a filter-fitting adapter and your old aerator to your local home improvement store to then match both to the...
