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Earlier editions: 20222019

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/LEACHING
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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