Recommended Brita filter for post-softener use
In a home with a whole-home water softener, the Brita Longlast+ filter (model OBB-01, 120-gallon rating, NSF 42/53) is the appropriate choice. The Longlast+ provides lead reduction (NSF 53) -- important because softeners do not remove lead, and older home plumbing may have lead solder joints that the softener cannot protect against. The Longlast+ also reduces copper and mercury in the post-softener supply.
The Brita Standard filter (40-gallon, NSF 42 only) is acceptable if lead is not a concern. In post-softener water the Standard filter may last slightly longer than 40 gallons due to reduced hardness fouling -- however, Brita specifies 40 gallons as the maximum for safety reasons (bacteria growth prevention in spent carbon media), not just capacity depletion. Do not exceed the 40-gallon limit regardless of taste.
Filter replacement timing
Standard Brita filter: replace every 40 gallons or every 2 months (whichever comes first). Longlast filter: replace every 120 gallons or every 6 months. These intervals are manufacturer minimums and should not be extended, even in softened water. A used carbon filter is a growth medium for bacteria -- the 40-gallon and 120-gallon limits account for microbiological safety, not just filtration performance. Use the Brita electronic indicator on compatible pitchers and check taste monthly.
Testing softened water at the Brita fill tap
After softener installation, test the cold kitchen tap water with a hardness test strip before refilling the Brita pitcher. Target: 0-3 GPG. If the test shows above 3 GPG: the softener is not conditioning the water correctly -- check salt level, control valve settings, and bypass valve position. Hard water reaching the Brita pitcher will shorten filter life back to pre-softener rates and negate the scale benefits of the softener installation.