Water Conditioning (C-55) · Lesson 3 of 5

Softener Efficiency and Hardness Limits (CPC Appendix L)

"Softener Efficiency and Hardness Limits (CPC Appendix L)" is lesson 3 of 5 in the Water Conditioning (C-55) Learning Hub. It opens with "Know the Status of Appendix L" and works through 6 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. Know the Status of Appendix L
  2. The Two Hardness Thresholds
  3. The Efficiency Limits on the Softener Itself
  4. Turn Hardness Into a Daily Load
  5. Convert the Load Into Salt and Wastewater Caps
  6. Other Treatment Devices in Appendix L

The worked example in the course applies this lesson to a realistic job in 6 steps, from "Check the thresholds" through "Wastewater cap".

What you'll be able to do

  • Explain the main idea of "Softener Efficiency and Hardness Limits (CPC Appendix L)" in plain language you can use on the exam.
  • Apply this step with confidence: "The Efficiency Limits on the Softener Itself".
  • Apply this step with confidence: "Turn Hardness Into a Daily Load".
  • Apply this step with confidence: "Convert the Load Into Salt and Wastewater Caps".
  • Apply this step with confidence: "Other Treatment Devices in Appendix L".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Softener Efficiency and Hardness LimitsHARDNESS (grains per gallon, as CaCO3)8901815 (sample)≤ 8: no softener discharge, residential (L410.2)≥ 9: rough-in for treatment, new 1-2 family (L502.6)Softener limits (L410.1):more than 3,400 grains per lb of salt, andno more than 4 gal per 1,000 grains removedWORKED NUMBERS250 gal/day x 15 gr/gal= 3,750 gr/day24,000 gr unit / 3,750= 6.4 days3,750 gr/day x 30 days= 112,500 grSalt: 112,500 / 3,400= 33.1 lb maxWaste: 112,500 / 1,000 x 4= 450 gal maxAssumed inputs (not from the code book):250 gal/day, 15 gr/gal, 24,000 gr capacityWhole-house use, 30 days (250 x 30)7,500 galSoftener wastewater limit, 30 days450 gal (6%)112,500 grains removed: under 33.1 lb salt and under 450 gal wastewaterAppendix L is not mandatory unless adopted: confirm with the local building departmentSource: 2025 California Plumbing Code Appendix L, Sections L 410.1, L 410.2, L 502.6CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: Know the Status of Appendix L

CPC Appendix L (Sustainable Practices) states that its provisions are not mandatory unless specifically adopted by a state agency, or referenced in the adopting ordinance. The adoption matrix printed in the copy on disk has no agency boxes marked, so treat these numbers as the printed California model-code criteria and confirm with the local building department whether the city or county has adopted them. California Green Building Code Appendix A5, Section A5.303.3 item 5, separately warns that water softeners that discharge to the community sewer may be limited or prohibited by local agencies.

Step 2: The Two Hardness Thresholds

CPC L 410.2 says that in residential buildings where the supplied potable water hardness is equal to or less than 8 grains per gallon (137 mg/L), measured as total calcium carbonate equivalents, water softening equipment that discharges water into the wastewater system during the service cycle shall not be allowed, except as required for medical purposes. CPC L 502.6 says that where hardness is equal to or exceeding 9 grains per gallon (154 mg/L), the water supply line to water heating equipment in new one- and two-family dwellings shall be roughed-in to allow for the installation of water treatment equipment. So you need the water test number before you quote a softener.

The remaining 4 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.

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