---
kind: "range"
citation: "40 C.F.R. §§ 141.530–141.536"
title: "40"
from: "141.530"
to: "141.536"
count: 7
url: "https://uscodex.org/cfr/40/141.530..141.536"
---

# §141.530. What is a disinfection profile and who must develop one?


A disinfection profile is a graphical representation of your system's level of Giardia lamblia or virus inactivation measured during the course of a year. If you are a [subpart H](/cfr/40/subpartH.md) community or non-transient non-community water system which serves fewer than 10,000 persons, your system must develop a disinfection profile unless your State determines that your system's profile is unnecessary. Your State may approve the use of a more representative data set for disinfection profiling than the data set required under [§§ 141.532-141.536](/cfr/40/141.532-141.536.md).


# §141.531. What criteria must a State use to determine that a profile is unnecessary?


States may only determine that a system's profile is unnecessary if a system's TTHM and HAA5 levels are below 0.064 mg/L and 0.048 mg/L, respectively. To determine these levels, TTHM and HAA5 samples must be collected after January 1, 1998, during the month with the warmest water temperature, and at the point of maximum residence time in your distribution system. Your State may approve a more representative TTHM and HAA5 data set to determine these levels.


# §141.532. How does my system develop a disinfection profile and when must it begin?


A disinfection profile consists of three steps:

- (a) First, your system must collect data for several parameters from the plant as discussed in [§ 141.533](/cfr/40/141.533.md) over the course of 12 months. If your system serves between 500 and 9,999 persons you must begin to collect data no later than July 1, 2003. If your system serves fewer than 500 persons you must begin to collect data no later than January 1, 2004.
- (b) Second, your system must use this data to calculate weekly log inactivation as discussed in §§ [141.534](/cfr/40/141.534.md) and [141.535](/cfr/40/141.535.md); and
- (c) Third, your system must use these weekly log inactivations to develop a disinfection profile as specified in [§ 141.536](/cfr/40/141.536.md).

# §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)](/cfr/40/141.74.md?p=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.

# §141.534. How does my system use this data to calculate an inactivation ratio?


Use the tables in [§ 141.74(b)(3)(v)](/cfr/40/141.74.md?p=b-3-v) to determine the appropriate CT99.9 value. Calculate the total inactivation ratio as follows, and multiply the value by 3.0 to determine log inactivation of Giardia lamblia:


# §141.535. What if my system uses chloramines, ozone, or chlorine dioxide for primary disinfection?


If your system uses chloramines, ozone, or chlorine dioxide for primary disinfection, you must also calculate the logs of inactivation for viruses and develop an additional disinfection profile for viruses using methods approved by the State.


# §141.536. My system has developed an inactivation ratio; what must we do now?


Each log inactivation serves as a data point in your disinfection profile. Your system will have obtained 52 measurements (one for every week of the year). This will allow your system and the State the opportunity to evaluate how microbial inactivation varied over the course of the year by looking at all 52 measurements (your Disinfection Profile). Your system must retain the Disinfection Profile data in graphic form, such as a spreadsheet, which must be available for review by the State as part of a sanitary survey. Your system must use this data to calculate a benchmark if you are considering changes to disinfection practices.