Chapter 15 — ALTERNATE WATER SOURCES FOR NONPOTABLE APPLICATIONS
1504.3 Determination of Maximum Absorption Capacity — 2025 California Plumbing Code
California Plumbing Code (Title 24, Part 5) · 2025 edition · updated 2026-09-25 · California
CBSC: official editions, supplements and errata
Italicized text is a California amendment to the model code, as printed in the official publication.
Cite as: 2025 California Plumbing Code (Title 24, Part 5) § 1504.3 · Effective January 1, 2026 · Official source: Building Standards Commission
Capacity. The irrigation field and mulch basin size shall be based on the maximum absorption capacity of the soil and determined using Table 1504.2. For soils not listed in Table
1504.2, the maximum absorption capacity for the proposed site shall be determined by percolation tests or another method acceptable to the Authority Having Jurisdiction. A gray water system shall not be permitted, where the percolation test shows the absorption capacity of the soil is unable to accommodate the maximum discharge of the proposed gray water irrigation system.
Exceptions:
(1) The Enforcing Agency may waive the requirement for identification of groundwater level and/or soil absorp- tion qualities based on knowledge of local conditions.
(2) Irrigation fields in compliance with Section 1504.5 which only utilize drip type emitters are exempt from percola- tion tests.
TABLE 1504.2
DESIGN OF SIX TYPICAL SOILS
| TYPE OF SOIL | MINIMUM SQUARE FEET OF IRRIGA- TION/ AREA PER 100 GALLONS OF ESTIMATED GRAY WATER DISCHARGE PER DAY |
MAXIMUM ABSORPTION CAPACITY IN GALLONS PER SQUARE FOOT OF IRRIGATION/ LEACHING AREA FOR A 24-HOUR PERIOD |
|---|---|---|
Coarse sand or gravel |
20 | 5.0 |
Fine sand |
25 | 4.0 |
Sandy loam |
40 | 2.5 |
Sandy clay |
60 | 1.7 |
Clay with consider- able sand or gravel |
90 | 1.1 |
Clay with small amounts of sand or gravel |
120 | 0.8 |
For SI units: 1 square foot = 0.0929 m [2], 1 gallon per day = 0.000043 L/s
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