The Water Pollution Control Act, enacted in 1970, regulates the discharge of water from factories and business establishments into public water bodies (rivers, lakes, ports, irrigation canals, public waterways, etc.

The Water Pollution Control Act, enacted in 1970, regulates the discharge of water from factories and business establishments into public water bodies (rivers, lakes, ports, irrigation canals, public waterways, etc.
Public Sewerage, Water Supply within the Watershed Excluded → Sewage System Act Applies) and prevents water pollution in public water bodies and groundwater. The most significant recent amendment was the 1996 "Basic Water Environment Plan," which included provisions for groundwater purification measures.
In addition to uniform standards, supplementary standards also exist for discharge. The discharge standards (tables on pages 22-23) are broadly divided into two categories with different scopes of application. Standards for the content of "hazardous substances" in discharged water apply to all discharges regardless of scale.
On the other hand, standards for "living environment items" (such as pH) in discharged water apply only to facilities with a daily average discharge volume exceeding 50 cubic meters. Facilities discharging less than 50 cubic meters per day are exempt (Note: As of July 1st, new items—"boron and its compounds," "fluorine and its compounds," "ammonia and ammonium compounds," and "nitrous acid and its compounds"—were added).
Furthermore, separate from the national standards, there are "supplementary standards" set by prefectural ordinances. These standards designate specific regions and establish stricter permissible limits than the uniform standards; currently, most prefectures have established such standards.
For example, Gunma Prefecture sets its discharge standard for biochemical oxygen demand (BOD) at 25 mg/l instead of the uniform standard of 160 mg/l, and its standard for suspended solids at 50 mg/l instead of 200 mg/l. Furthermore, prefectures can establish regulations via ordinances for items not covered by the uniform standards or for facilities without specific designated areas (horizontal extension standards).
Furthermore, Tokyo Bay, Ise Bay, and the Seto Inland Sea are designated as special water areas. Prefectures designate regions within these areas that generate pollution loads flowing into them and set standards for specific facilities within those regions.
Separate standards exist for the infiltration of water containing harmful substances into the ground. Groundwater infiltration standards, such as 0.001 mg/l for cadmium and its compounds and 0.1 mg/l for cyanide compounds, are stricter than the discharge standards. It is important to note that these infiltration standards apply not only to public water bodies but also to businesses discharging into groundwater.
Applicable businesses are obligated not only to comply with discharge standards but also to fulfill the following requirements: 1. Notification of Designated Facilities. When establishing a new designated facility or making structural changes to an existing one, notification must be submitted to the prefecture before the change occurs. The change must be completed within 100 days of the acceptance date of the installation or change notification.
Notification must be made within 30 days if a facility is newly designated as a specified facility, if the representative or facility name changes, or if the specified facility is sold, transferred, leased, or its status is succeeded. 2. Measurement and Record Keeping. Applicable operators must measure the quality status of discharged water and infiltrated groundwater and retain records of these measurements. However, while measurement and record-keeping are mandatory, submission of this information is not required.
3. Emergency Measures. If water containing hazardous substances is discharged into public waterways or infiltrates the ground due to facility damage or other accidents, prompt emergency measures must be taken and reported to the prefectural government. Hazardous substances include crude oil, fuel oil, lubricating oil, light oil, kerosene, volatile organic compounds, and animal/vegetable oils.
4. Groundwater Remediation Orders. If a local government determines that harmful substances from a specific facility have infiltrated the ground and are affecting or may affect human health, it may order the specific operator to remediate the groundwater. The remediation level is based on water quality environmental standards, but standards from the year the specific facility was established are not applied retroactively.