4. Water quality
(1) History of Drinking Water Quality Standards
The Waterworks Ordinance (the “old Waterworks Act” ) of 1890 did not include provisions for drinking water quality standards (DWQS). In 1908, the Council on Waterworks laid down the “Agreed Method of Water Examination” as the national standard method for inspecting water quality. In 1958, the DWQS were established based on the current Waterworks Act, which was enacted in the previous year. After minor amendments in 1960, 1966, and 1978, the standards went through a substantial amendment in 1992. In May 2003, about 10 years after the previous amendment, the standards were revised in response to the amendment to the Guidelines for Drinking Water Quality of the World Health Organization (WHO).
When the Waterworks Act was enacted in 1958, twenty-nine items were set as the first DWQS. Since then, the Ministry of Health (the predecessor of the Ministry of Health, Labour and Welfare) has made a series of amendments on the standards to comply with the latest scientific knowledge. Among those amendments, the one conducted in 1992 was especially significant. The standard items were increased from 26 to 46 in order to substantially reinforce and enhance drinking water quality management.
(2) Fundamental Principle of the Current DWQS
In July 2002, in response to the undergoing discussion of the 3rd Guidelines for WHO's Drinking Water Quality Guidelines, the ministry consulted with the Health Science Council on Japan's basic concept of Drinking Water Quality Standards revision.
A special committee for water quality (chaired by Professor Magara) was formed to discuss the concept of the revision of standards as well as the water quality management systems such as examination frequency. In April 2003, according to the report submitted by the council and the result of public comments, the new standards and the water quality management systems were formed and went into effect in April 2004.
Before this amendment, the DWQS were set only for items that are commonly seen throughout the nation as cause of the problems. For problems that are seen only locally or in the specific water purification methods, governmental instructions were made as a form of administrative guidance. In the amendment, such principles were reconsidered, and new standards were established based on the two fundamental principles below.
Firstly, the standards are set for all items that have the possibility to cause an adverse effect on human health or living condition regardless of the specialty of the locality, types of water source, or purification methods, even if the detection level of these items is low on a national basis. Secondly, water utilities are obliged to carry out drinking water quality examination only for the basic items and may omit some of the non-basic items from analysis according to their local situation. To make their examination appropriate and transparent the new system requires each water utilities to prepare ‘Annual Water Quality Examination Plan’ that indicates the boundaries for analysis, and to publish their plans for water consumers beforehand.
Diagram 12 shows the scheme of the drinking water quality control in Japan. As shown in the diagram, three-layered group forms a pyramid-shaped structure.
Diagram 12 Scheme of Drinking Water Quality Control
The group on the top of the pyramid is the legally binding standards. Around thirty items are set from the viewpoint of human health, and around twenty items are set from the viewpoint of other reasons including user needs regarding water quality. These items are selected for their detection rate (over 10% of the standards value) in purified water in Japan. The Waterworks Act requires the water utilities to monitor tap water quality regularly in order to make sure that water meets the standards.
The middle group is items not-legally binding with target values. Those items are set to complement the standards and the Ministry encourages water utilities to monitor and achieve the targets. The bottom group contains a list of items that require further study for risk assessment and a grip of detection level. The DWQS is to be updated by rolling revision according to scientific knowledge, with consideration of health-based value such as TDI, detection rate, and progress of treatment technology.
Since 2004, the standards were continuously revised and current DWQS includes 51 items as shown in Diagram13.
Diagram13 Drinking Water Quality Standards(PDF:48KB)
Complementary items are shown in Diagram14. Those items were also revised continuously.
Diagram14 Target value for complementary items(PDF:48KB)
(3) Control of Pathogenic Organisms
As mentioned in the “Overview of Water Supply Services”, the number of the patients suffering from waterborne diseases has decreased rapidly by the introduction of disinfection. The coverage of water supply as of 2006 is more than 97% with very few patients.
This result indicates that disinfection is effective for preventing waterborne diseases. Moreover, even after ordinal treatment process, such as sedimentation and sand filtration, there still remains a possibility of contamination with bacteria. Also, water can be contaminated in the process of distribution, since bacteria can enter pipes due to low pressure or breaks in pipes.
The Act requires that tap water contains more than 0.1 mg/L of residual chlorine, and on a daily basis, the inspection has to be conducted at taps at the end of distribution network.
Even now, some infectious diseases caused by drinking water were reported almost every year. But many of them occurred at very small-scale water utility because of inappropriate management or inefficient disinfection.
Currently, one of the greatest concerns in this field is how to deal with chlorine-resistant pathogens such as Cryptosporidium and Giardia.
In June 1996, an outbreak of cryptosporidiosis occurred in Ogose Town (Saitama Prefecture) and 8,800 cases were reported. This was the first incident associated with a public water supply in Japan. In this case, more than 70% of the community population reported severe diarrhea. The cause of the outbreak confirmed insufficient management of purification process.
In October 1996, the Ministry of Health, Labour and Welfare issued the tentative guidelines for cryptosporidium treatment in waterworks (Revised in 1998 and 2001). In March 2007, the newly revised guideline (not tentative), “The guidelines for cryptosporidium treatment in waterworks”, was published. The guideline suggests that water utilities assess the risk level of potential contamination of each water treatment plant. Risk level is assessed by the detection of indicator organisms in raw water and the type of the raw water as shown in Diagram 15.
Diagram 15 Determination of Risk Level
The guideline also shows necessary preventive measures for each risk level. If a water treatment plant is categorized as Level-4 or Level-3, water supplier is expected to apply countermeasures. As shown in Diagram 16, for Level-4 plant, it is required to keep turbidity of filtered water to less than 0.1 degree and for Level-3 plant, it is required to follow same measures as Level-4 or install UV irradiation system.
Diagram 16 Required facilities
(4) Water Safety Plan
The concept of Water Safety Plan (WSP) was proposed by WHO in its 3rd Guideline for Drinking Water Quality issued in September 2004. The plan is a management tool, which introduces a comprehensive risk assessment and risk management approach encompassing all steps in water supply.
WSP's essential concepts are as follows:
1. Identify hazards (including potential hazards) from all steps in water supply system and evaluate each hazard's risk level. According to the risk level, identify critical control points and prioritize the response measures to be taken.
2. Conduct constant monitoring of operational aspect of facilities (Not only tap water quality - monitor and maintain its performance level at all critical control points)
WSP applies HACCP (Hazard Analysis and Critical Control Points) methods to the water supply. HACCP is a system which is used in the food industry for identifying and controlling known food safety hazards and critical control points. It enhances safety through a systematic, science-based program. In the food industry, before the introduction of HACCP, surprise investigation was employed.
The objectives of WSP are to minimize contamination of source water, to remove contamination through treatment, and to prevent re-contamination during storage, distribution and handling of drinking water on the basis of multiple-barrier approach.
Introduction of WSP is expected to result in effects such as the following:
- Unified identification and evaluation of water supply systems
- Reduction of risks and improvements in safety
- Re-evaluation of systems by means of objective methods
- Elimination of unfounded assumptions
- Improvement and streamlining of maintenance and control levels
- Clarification of priority regarding crucial control points
- Improvement of operators' maintenance and control ability
- Transfer of technology to the next generation (through unified documentation)
- Improvement of communications with concerned third parties
- Increase of accountability on water safety to consumers
- Approach to watershed areas-related stakeholders in order to secure better water quality at water sources
The Ministry of Health, Labour and Welfare compiled the guideline for introduction of WSP and the guideline was delivered to drinking water utilities in May 2008.