40 CFR § 141.533 - What data must my system collect to calculate a disinfection profile?

---
identifier: "/us/cfr/t40/s141.533"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "40 CFR § 141.533 - What data must my system collect to calculate a disinfection profile?"
title_number: 40
title_name: "Protection of Environment"
section_number: "141.533"
section_name: "What data must my system collect to calculate a disinfection profile?"
chapter_name: "ENVIRONMENTAL PROTECTION AGENCY"
subchapter_number: "D"
subchapter_name: "WATER PROGRAMS"
part_number: "141"
part_name: "NATIONAL PRIMARY DRINKING WATER REGULATIONS"
positive_law: false
currency: "2026-04-05"
last_updated: "2026-04-05"
format_version: "1.1.0"
generator: "[email protected]"
authority: "42 U.S.C. 300f, 300g-1, 300g-2, 300g-3, 300g-4, 300g-5, 300g-6, 300j-4, 300j-9, and 300j-11."
regulatory_source: "40 FR 59570, Dec. 24, 1975, unless otherwise noted."
cfr_part: "141"
---


# 141.533 What data must my system collect to calculate a disinfection profile?

Your system must monitor the following parameters to determine the total log inactivation using the analytical methods in § 141.74 (a), once per week on the same calendar day, over 12 consecutive months:

(a) The temperature of the disinfected water at each residual disinfectant concentration sampling point during peak hourly flow;

(b) If your system uses chlorine, the pH of the disinfected water at each residual disinfectant concentration sampling point during peak hourly flow;

(c) The disinfectant contact time(s) (“T”) during peak hourly flow; and

(d) The residual disinfectant concentration(s) (“C”) of the water before or at the first customer and prior to each additional point of disinfection during peak hourly flow.