40 CFR § 141.521 - What updated watershed control requirements must my unfiltered system implement to continue to avoid filtration?

---
identifier: "/us/cfr/t40/s141.521"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "40 CFR § 141.521 - What updated watershed control requirements must my unfiltered system implement to continue to avoid filtration?"
title_number: 40
title_name: "Protection of Environment"
section_number: "141.521"
section_name: "What updated watershed control requirements must my unfiltered system implement to continue to avoid filtration?"
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"
---


# 141.521 What updated watershed control requirements must my unfiltered system implement to continue to avoid filtration?

Your system must take any additional steps necessary to minimize the potential for contamination by *Cryptosporidium* oocysts in the source water. Your system's watershed control program must, for *Cryptosporidium*:

(a) Identify watershed characteristics and activities which may have an adverse effect on source water quality; and

(b) Monitor the occurrence of activities which may have an adverse effect on source water quality.