It is the top of this page

About radioactive material in tap water

Last update date March 12, 2020

About safety of tap water

About the inspection system of Yokohama-shi

About test result

About clean water outbreak soil

About safety of tap water

Q
1.Can tap water of Yokohama-shi drink?
A

As for the tap water of Yokohama-shi, drinking does not have trouble.

Management target value of radioactive material in tap water is "10 becquerels/kg" (total value of cesium 134 and 137).
It is the non-detection (detection limit level 1 becquerel/kg or less), and test result of tap water of three water purification plant (Kawai, Nishiya, willow tit) in Yokohama-shi and radioactive cesium of water supply Haramizu is less than management target value.

Q
2.What is regulation of radioactive material in tap water?
A

From April 1, 2012, new management target value "10 becquerels/kg" (total value of cesium 134 and 137) is set.

From April 1, 2012, new standard in the food hygiene law was set about radioactive material in food including drinking water and was changed to "10 becquerels/kg" from past 200 becquerels/kg about radioactive cesium in drinking water.
We received this change, and, about tap water, "10 becquerels/kg" (total value of cesium 134 and 137) was set as management target value of radioactive material in tap water by notice of Ministry of Health, Labour and Welfare. In addition, about radioactive iodine, new management target value is not set because half-life is short (about eight days).

※Notice of Ministry of Health, Labour and Welfare health station Channel section manager dated March 5, 2012 (": 172KB) (PDF about setting of management target value to affect radioactive material in tap water" "in detail: 226KB) (PDF")

Index level about radioactive material in tap water and management target value
Date Index level and management target value

Index level (target value)
(unit: becquerel /kg)
[radioactive iodine]

Index level (target value)
(unit: becquerel /kg)
[radioactive cesium]

March, 2011 Index level about food and drink intake restriction
(provisional criteria about baby/infant)
300
(100)
200
April, 2012 Management target value of tap water 10
Q
3.When radioactive cesium more than management target value is detected, what happens?
A

We are the cause and study and will tell water supply user.

Even if the density of radioactive material in tap water is beyond management target value (10 becquerels/kg), it is not meaning not to be suitable for drinking.
But when radioactive cesium is beyond target value, we are the cause promptly and study and will tell water supply user for relief, security.

※Notice of Ministry of Health, Labour and Welfare health station Channel section manager dated March 5, 2012 (": 172KB) (PDF about setting of management target value to affect radioactive material in tap water" "in detail: 226KB) (PDF")

About the inspection system of Yokohama-shi

Q
4.What happens to the inspection system of City of Yokohama, Water Works Bureau?
A

We secure detection limit level 1 becquerel/kg or less and inspect tap water of three water purification plant in Yokohama-shi and water supply natural water.

In City of Yokohama, Water Works Bureau, we carry out inspection of radioactive material about tap water of three water purification plant (Kawai, Nishiya, willow tit) in Yokohama-shi from March 19, 2011.

In City of Yokohama, Water Works Bureau, we introduced germanium semiconductor detector newly in June, 2012.
We secure detection limit level 1 becquerel/kg or less and expand the system to be able to give a test with high precision and inspect radioactive material for each cesium 134 and cesium-137 precisely by using germanium semiconductor detector.
We are inspecting tap water of three water purification plant (Kawai, Nishiya, willow tit) in Yokohama-shi and water supply natural water at monthly frequency now.
In addition, we inspect tap water of periodical examination of water point of 15 city at monthly frequency.

※It is Q5 about germanium semiconductor detector

The radiological inspection system of tap water of City of Yokohama, Water Works Bureau
Date Event Inspection frequency Inspection organization
March 11, 2011 The Great East Japan Earthquake occurrence - -
March 19 We start inspection of tap water of Yokohama-shi Every day Yokosuka-shi Waterworks and Sewerage Bureau
August 1
(until March 31, 2012)
We start inspection in City of Yokohama, Water Works Bureau Every day City of Yokohama, Water Works Bureau
January 4, 2012 We start inspection using germanium semiconductor detector Kawai, Nishiya, willow tit water purification plant each once in three weeks Yokohama City Inst. of Health
April 2 We start inspection based on new management target value (10 becquerels/kg) Once a week Wide area Channel company group in Kanagawa
June 5 We introduce germanium semiconductor detector into City of Yokohama, Water Works Bureau and start inspection Twice a week City of Yokohama, Water Works Bureau
August 7 - Once a week City of Yokohama, Water Works Bureau
After January, 2014 - Once a month City of Yokohama, Water Works Bureau

※Summary of past test result is Q10

Q
5.What is germanium semiconductor detector?
A

Inspection of high sensitivity that is with detection limit level 1 becquerel/kg or less of is possible inspection equipment.

About each cesium 134 and cesium-137, we secure detection limit level 1 becquerel/kg or less by using germanium semiconductor detector, and sensitive inspection is possible.

suisitsu-20120601-geruma1.jpg
State of inspection with germanium semiconductor detector

suisitsu-20120601-geruma2.jpg
It looks like we set sample in the detector inside

Q
6.Does inspection frequency include standard?
A

"As a general rule, it is said more than once a month" by notice from Ministry of Health, Labour and Welfare.

Inspection frequency is notified by Ministry of Health, Labour and Welfare saying, "as a general rule, but we inspect by the above depending on the inspection systems such as water supply companies more than once a month once a week till enough information in high turbidity such as the rain, thaw is collected".

※Notice of Ministry of Health, Labour and Welfare health station Channel section manager dated March 5, 2012 (": 172KB) (PDF about setting of management target value to affect radioactive material in tap water" "in detail: 226KB) (PDF")

Q
7.Do we not need to inspect every day?
A

We think that we can secure safety for radioactive cesium by turbidity management and periodical inspection.

We received accident of Fukushima Daiichi Nuclear Power Station of 2011 and carried out inspection at the above-mentioned frequency in City of Yokohama, Water Works Bureau once a week until December, 2013. As a result of past inspection, we are never detected about radioactive cesium including time when turbidity of water supply Haramizu rose in typhoons by tap water of Yokohama-shi and water supply natural water. Because enough information about the tendency was collected about tap water and radioactive cesium of water supply Haramizu, we did inspection frequency more than once a month from January, 2014.
In addition, we can remove radioactive cesium with cloudiness in process of clean water processing of water purification plant because ingredient of cloudiness includes the most in water supply Haramizu.
We will carry out turbidity management thoroughly in future and think that by confirming by periodical inspection, can secure safety for radioactive cesium.

Q
8.May you change inspection frequency in future?
A

We increase inspection frequency and, depending on the situation, strengthen monitoring of radioactive material.

We carry out inspection along inspection frequency shown by notice of Ministry of Health, Labour and Welfare in City of Yokohama, Water Works Bureau.
But cases that occurred increase inspection frequency, and some kind of abnormality strengthens monitoring to radioactive material for clean water processing process in water purification plant again when release of newly large-scale radioactive material will occur in future.

Q
9.Do you inspect radioactive material except radioactive cesium?
A

We do not inspect material except radioactive cesium because we can confirm safety of all the radioactive materials which by inspecting radioactive cesium, become a target of regulation.

As for the radioactive material becoming a target of regulation other than radioactive cesium, it is revealed that density is low by survey by Ministry of Education, Culture, Sports, Science and Technology very much in comparison with radioactive cesium.
Management target value (10 becquerels/kg) of radioactive cesium which Ministry of Health, Labour and Welfare set is set after having considered other radioactive material. It is not necessary to perform inspection of material except radioactive cesium some other time because we can confirm safety about all the radioactive materials which by inspecting radioactive cesium, become a target of regulation.

※Notice of Ministry of Health, Labour and Welfare health station Channel section manager dated March 5, 2012 (": 172KB) (PDF about setting of management target value to affect radioactive material in tap water" "in detail: 226KB) (PDF")

About test result

Q
10.How does test result of conventional radioactive material turn out?
A

After March 25, 2011, radioactive material has not been detected by tap water.

In City of Yokohama, Water Works Bureau, we carry out inspection of radioactive material about tap water of three water purification plant in Yokohama-shi from March 19, 2011.
By past result, all radioactive cesium was less than detection limit level and have not been detected.
In addition, radioactive iodine was detected by tap water of some water purification plant supplying with water in Yokohama-shi for three days from March 22, 2011 just after earthquake disaster to 24th, but is not detected on after March 25.

Summary (unit: becquerel /kg) of radiological test result in tap water
Date Event Test sample Test result Detection limit level
March 11, 2011 The Great East Japan Earthquake occurrence
March 19 Inspection start of tap water of Yokohama-shi All water purification plant which supply with water in Yokohama-shi The non-detection About ten
March 22 Radioactive iodine is detected by tap water Willow tit water purification plant 55.3 About ten
March 22 Radioactive iodine is detected by tap water Ayase water purification plant (wide area Channel company group in Kanagawa) 13.7 About ten
March 23 Radioactive iodine is detected by tap water Willow tit water purification plant 56.8 About ten
March 23 Radioactive iodine is detected by tap water Kawai water purification plant 11.9 About ten
March 23 Radioactive iodine is detected by tap water Ayase water purification plant (wide area Channel company group in Kanagawa) 55.7 About ten
March 23 Radioactive iodine is detected by tap water Sagamihara water purification plant (wide area Channel company group in Kanagawa) 18.4 About ten
March 23 Radioactive iodine is detected by tap water The west Nagasawa water purification plant (wide area Channel company group in Kanagawa) 9.2 About ten
March 24 Radioactive iodine is detected by tap water Willow tit water purification plant 23.5 About ten
March 24 Radioactive iodine is detected by tap water Kawai water purification plant 8.8 About ten
March 24 Radioactive iodine is detected by tap water Ayase water purification plant (wide area Channel company group in Kanagawa) 21.4 About ten
March 24 Radioactive iodine is detected by tap water Sagamihara water purification plant (wide area Channel company group in Kanagawa) 12.5 About ten
After March 25 We non-detect in both tap water All water purification plant which supply with water in Yokohama-shi The non-detection About ten
January 4, 2012 Inspection start using germanium semiconductor detector Three water purification plant in Yokohama-shi The non-detection About one
After April 2 Inspection start using germanium semiconductor detector All water purification plant which supply with water in Yokohama-shi The non-detection About one

All water purification plant which supply with water in note) Yokohama-shi
Kawai water purification plant, Nishiya water purification plant, willow tit water purification plant (City of Yokohama, Water Works Bureau)
Ayase water purification plant, Sagamihara water purification plant, the west Nagasawa water purification plant (wide area Channel company group in Kanagawa)

※The past inspection system (the frequency, measurement organization) is Q4

Q
11.What do you mean with "the non-detection" (detection limit level 0 0) of test result?
A

We mean that inspection equipment of radioactive material is less than the detectable minimum density.

"The non-detection" (detection limit level 0 0) means that radioactive material concentration in tap water which we inspected is less than detection limit level (the minimum density that device inspecting radioactive material is detectable).
If test result is "the non-detection" (detection limit level 0 0), radiological density "is less than 0 0".

Q
12.Why is it that detection limit levels are slightly different?
A

It is slightly different every time in state or surrounding environment of inspection equipment.

We carry out inspection closely, but detection limit level is slightly different every time in state or surrounding environment of inspection equipment because it is very exact inspection. At every inspection, we calculate detection limit level at that time (the detectable minimum density).

About clean water outbreak soil

Q
13.What is clean water outbreak soil?
A

We collected the earth and sand in water supply natural water and impurities such as cloudiness.

Tap water is made from water of lake and river. The earth and sand or cloudiness are included in water of this lake and river.
Clean water outbreak soil is impurities such as the earth and sand or cloudiness to remove when we purify water supply natural water (water of lake and river) and make tap water.

Q
14.Why is it that radioactive cesium is detected with clean water outbreak soil?
A

This is because impurities such as cloudiness in water supply Haramizu are concentrated by high density.

Ingredient of cloudiness includes the most in water supply Haramizu, and radioactive cesium is removed with cloudiness in process of clean water processing of water purification plant.
Water supply Haramizu of 20,000-26,000 liters is handled before 1 kg of clean water outbreak soil occurs (as for the mean quantity of water that ordinary household uses for one month 15,000 liters). In other words, impurities such as cloudiness in water supply Haramizu are concentrated to 20,000-26,000 times.
In addition, radioactive material is not detected from tap water after March 25, 2011.

Q
15.How do you dispose of clean water outbreak soil in City of Yokohama, Water Works Bureau?
A

We reuse as cement raw materials from September, 2011.

At City of Yokohama, Water Works Bureau Nishiya water purification plant, we reused the earth and sand occurring by clean water disposal of Kawai water purification plant and Nishiya water purification plant as material on gardening Doyo, but we receive accident of Fukushima Daiichi Nuclear Power Station and restrain ourselves from the use as gardening soil.
Because the situation less than standard (100 becquerels/kg) that the density of radioactive cesium included in clean water outbreak soil established in country continued after August, 2011, we reuse as cement raw materials from September, 2011.
In addition, we put provisionally in sludge disposal of Nishiya water purification plant facility, and the earth and sand generated before September kept, but completed disposal by the end of 2011.
In addition, we treat the earth and sand generated at willow tit water purification plant appropriately in the City of Yokohama, Environmental Planning Bureau southern part sludge exploitation of resources center.

Q
16.What is regulation about clean water outbreak soil?
A

If the radioactive cesium totals are 8,000 becquerels/kg or less, we fill up, and disposal is possible.

If the radioactive cesium totals are 8,000 becquerels/kg or less, according to the notification of Ministry of Health, Labour and Welfare, inning disposal is enabled in management type disposal ground.
In addition, thing which becomes standard or less (as for the reuse to concrete 100 becquerels/kg) before circulating in market becomes reusable.
In addition, about the use to gardening Yodo, it becomes when it is appropriate to restrain from shipment of product.

※Director Ministry of Health, Labour and Welfare health notification "(the outside site) about way of thinking about the present handling of detected clean water generating soil radioactive material" dated June 16, 2011

Related link

Inquiry about water supply to Water Works Bureau customer Service Center

Water Works Bureau customer Service Center

Telephone: 045-847-6262 fax: 045-848-4281
※You run, and please be careful not to make any mistake

Adobe Acrobat Reader DC (old Adobe Reader) is necessary to open file of Portable Document Format.
Person who does not have can download free of charge from Adobe company.
Get Adobe Acrobat Reader DCTo downloading of Adobe Acrobat Reader DC

Inquiry to this page

The Water Works Bureau clean water part quality of the water section

Telephone: 045-371-5656

Telephone: 045-371-5656

Fax: 045-371-6942

E-Mail address [email protected]

Return to the previous page

Page ID: 209-577-552

We come back to the top