The cost of water filter and softening system installation in Downey varies depending on the size and type of system, as well as installation fees and any additional plumbing work that may be required. On average, a whole-house system can cost between $1,000 and $3,000, while a point-of-use system can cost between $100 and $500. Consult with a professional plumber to get an accurate estimate for your specific installation.