Frequently Asked Questions and Answers
About water examination
A; The water quality of tap water is required to satisfy the water quality standards prescribed by the Waterworks Law.
In order to always supply potable delicious water to our customers, the Bureau of Waterworks carries out detailed water quality management from the water resource to taps.
A; The Bureau of Waterworks ensures the safety of tap water through regular water quality examination. The results are published on our website, collected in the “Annual Water Quality Report”, and supplied to Citizens Information Rooms and other places.
A; The Bureau of Waterworks will carry out examinations of water quality at the request of customers who feel something is wrong.
In locations such as apartment buildings and collective housings, where tap water is piped to individual apartments from a receiving tank, the Public Health Center may also conduct testing of the water. Please contact the customer service center for advice about your individual circumstances.
About safety of tap water
A; Chlorine is added to tap water to disinfect it. This is effective in killing pathogenic bacteria but has no effect on human beings.
Further, according to the WHO (World Health Organization) guidelines for drinking water quality, the recommended guideline value for chlorine in tap water is 5 mg/L. Concentrations of chlorine present in tap water at or below that value will have no effect on human health even if a person drinks the water in question for their entire life.
At the Tokyo Metropolitan Bureau of Waterworks, we normally manage the residual chlorine concentration to ensure that it is above the minimum limit of 0.1 mg/L set by the Waterworks Law, and below the value of 1 mg/L, which is the maximum value set in complementary items for water quality management.
A; River water contains organic substances derived from the decomposition of plants and also from waste water. The process of creating tap water involves treatment of the raw water with chlorine. These organic substances react with the chlorine to form trihalomethane. In Tokyo, the volume of all trihalomethane contained in the tap water is carefully managed to ensure it remains at a safe level below the maximum limit specified in the water quality standards, so there is no negative effect on human health.
Also, the maximum limits for various substances contained in the water quality standards have been established at levels that will not have a negative effect on human health even if a person continues to ingest the substances over their entire lifetime.
A; Cryptosporidium is a pathogen capable of infecting humans and livestock, but can be removed by conducting proper water treatment to remove impurities from the raw water. In order to ensure the safety of tap water, the Bureau of Waterworks strictly controls the degree of turbidity present in the water that leaves the purification plant, as well as conducting examinations to detect cryptosporidium. So you can relax and drink tap water secure in the knowledge that we have ensured it is free from cryptosporidium.
A; Dioxins are said to be created by activities such as side reactions of chemosynthesis incinerating waste and bleaching pulp. The Bureau of Waterworks, has been carrying out factual investigations for dioxins since 1997, but the amounts detected have been well below the target values contained in the supplements to the water quality standards. Going forward, we will continue to carry out thorough monitoring so that our customers can use tap water with peace of mind.
A; Asbestos cement pipes used in waterworks were found to have insufficient material strength so, as a precaution against earthquakes and to prevent leaks, these pipes were progressively replaced from 1973 onwards.
The result was that in the 23 wards of Tokyo replacement was complete by 1997, and in the Tama district, for the most part, by 2007. In regard to the effect on health, the Ministry of Health, Labour and Welfare announced in the “Health Effects of Water Passing Through Asbestos Cement Pipes” (July 13, 2005) report, the following conclusions:
1) The toxicity of asbestos was evaluated as part of the examination of the tap water quality standards, which were revised in 1992. The toxicity of asbestos ingested orally is very small compared with that breathed into the lungs. Also asbestos was not found to be present in tap water at dangerous levels, so there was no need to set up a specific water quality standard in relation to it.
2) Even in the guidelines set by the World Health Organization (WHO) for drinking water, in regard to the presence of asbestos in drinking water, the guidelines state: “There is, therefore, no consistent evidence that ingested asbestos is hazardous to health, and thus it is concluded that there is no need to establish a health-based guideline value for asbestos in drinking-water.”.
In this way, the relevant institutions, both inside Japan and abroad, do not see any evidence of adverse effects on human health caused by the presence of asbestos in tap water.
A; The results of the Bureau of Waterworks’ investigations is that norovirus was not detected in the water supply, and that even if norovirus was present in the river water that is the source of the water supply, it had been eliminated by water treatment, ensuring that the resulting tap water was safe to drink.
A; We have heard many reports of salespersons adding chemicals that react to the chlorine in the tap water, turning the water yellow or pink, in order to create a feeling of unease in customers that the water might contain harmful chemicals. This reaction doesn’t actually show that the water supply is dangerous, so do not be fooled.
A; When the water evaporates, the minerals contained in the water become white.Minerals will remain if you leave the water drops to evaporate.This can be prevented by wiping the water as much as possible.This phenomenon may also happen to humidifiers as well, and we recommend for you to exchange the water before it runs out. The same phenomenon will occur as well with mineral water. In this way, the white residues are minerals, and they are harmless.
A; When water freezes, a phenomenon occurs where the water component freezes gradually from the outside in, and the air and minerals dissolved in the water are concentrated in the center. When this ice melts, the air that is collected in this central portion escapes to join the atmosphere, but a portion of the minerals will have changed to substances that do not dissolve in water and so will be left behind as a white substance.
Also, depending on the way the ice was frozen, the mineral component may be gathered on the surface of the ice, and when the ice floats in water, the minerals may peel off the surface of the ice in white flakes.
Because this white substance is simply the remains of the air and minerals that were dissolved in the water, it is completely harmless and there is no reason to worry.
About activities to improve the taste of water
A; Everybody’s taste is different, so there is no common factor that decides what makes water tastes good. However, in 1985, the Ministry of Health and Welfare (now the Ministry of Health, Labour and Welfare) established a “Better Tasting Water Research Group” to put together the conditions for providing “good tasting water”. According to the result of this research, it was the presence of mineral components and carbon dioxide in the right quantities that was identified as producing better tasting water.In addition to other factors that make water taste better when drunk, there is also the issue of the temperature of the water. Water was found to taste better when it was at a temperature of between 15 and 20˚C when drunk.
A; The amount of calcium and magnesium that make up the mineral component of water when converted to calcium carbonate is called hardness. Hardness has an influence on the taste of the water. Hard water leaves an aftertaste in the mouth, and water whose hardness is too low is called soft water, which has no body. Water with an appropriate level of hardness is said to have a mellow taste.
Water that tastes good is expected to have an appropriate level hardness. Depending on the season and the water system, in general water in Tokyo has a hardness between 50 to 100 mg/L.
A; Advanced water treatment is intended to treat substances that cause a musty odor, substances that form trihalomethane, and ammonium nitrogen, that causes an odor of chlorine, because all substance and compounds cannot be sufficiently removed by ordinary water treatment, such as the rapid sand filtration. Bureau of Waterworks Tokyo Metropolitan has introduced advanced water treatment systems on the Tone River System (the Kanamachi, Misato, Asaka, Misono and Higashi-murayama Purification Plants) in October 2013. In these plants, ozonation treatment and biologically activated carbon adsorption treatment are incorporated between sedimentation basin and rapid filter basin.
A; The Bureau of Waterworks carries out disinfection using chlorine from a hygiene perspective and maintains a residual chlorine concentration of at least 0.1 mg/L at taps, in accordance with the requirements of the Waterworks Law. The Tokyo Metropolitan Bureau of Waterworks has independently established “Water Quality Target for Better Tasting Water” which specify a minimum necessary residual concentration of at least 0.1 mg/L and no more than 0.4 mg/L. In order to achieve this target, 131 automatic water quality meters in Tokyo check the water quality of the entire system to ensure that the amount of residual chlorine is maintained at an appropriate level.
Also, by installing additional chlorine injection equipment at the water supply stations that transmit and distribute water to various locations, it is possible to reduce the volume of chlorine added at water purification plants. So regardless of the distance to the water purification plants, the residual chlorine concentration is maintained as low as possible in the water that we provide.
In addition, we are working hard to provide safer and better tasting water through the introduction of advanced water treatment and the promotion of direct water supply system.
About domestic water filters
A; The Bureau of Waterworks maintains an appropriate level of quality in the water we supply in accordance with the water quality criteria of the Waterworks Law. So you can safely drink tap water as it is without needing to worry about anything. However, some people may want to use a domestic water filters because they are concerned about the smell of the chlorine that is used to disinfect the water. If you are using a domestic water filter, it is necessary to properly understand the features of the domestic water filter you are using. Also, because water remaining in the domestic water filter no longer contains chlorine, it is easier for bacteria to flourish there. So when using a domestic water filter, make sure you use it carefully and in accordance with the manufacturer’s directions.
A; There are various possible reasons for tap water having unusual color or smell. So if you notice anything unusual about the water coming out of your tap, you should first contact the customer service center for advice.
A; For information about the storage period for tap water, see here.
A; It may look blue when the water absorbs parts of the red lights along with the blue lights spreading upon the water.Water may become blue if it has elevated levels of copper, however more than 100 times the water quality standards of copper will be needed for this to happen.Usually this would not happen in a general home or resident.
A; It may be caused by an adhesion of copper soap. Copper soaps are produced when the copper ions from the copper pipes react with the soap products and scale deposits. Copper soap can be produced even if the copper levels are under the water quality standards. It is also formed from the copper eluted by the water heater and other similar appliances. This can be prevented by frequently washing out the soap and scale deposits to make sure that they do not remain.
A; Low concentrations of fluorine are effective in protecting against tooth decay, but on the other hand, problems have also been identified, such as where intake of too much fluorine causes dental fluorosis (condition where tooth enamel becomes mottled). For this reason, much debate has been carried out by the medical community over many years into the benefits versus the harm of adding fluorine to water, and no conclusion has been reached at the current time. The Bureau of Waterworks is paying close attention to these developments, and we will continue to make sure we are doing everything we can to supply safe and delicious water based on our established water quality criteria and available scientific knowledge.
A; In order to supply safe and delicious water, it is essential that the water quality of water resources must be maintained at as high a level as possible. Pollution of fresh water resources tends to be thought of as mainly the result of industrial waste discharged from factories. However liquid waste discharged from households is also a major cause of pollution. For example, one tablespoon of soy sauce discharged into a river, requires around 600 liters of water (around 3 bath tubs) to return the water quality to a level where fish can live in the river. Your efforts to reduce the amount of household wastewater you discharge is connected to keeping the resources of our drinking water clean.