Case

Turbid Water Prevention Efforts and Measures

Water utility(This is an example practiced by common water utilities in Japan)

General information of the utility (2019)*N/A = Not applicable

Operation
type

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Service area (km2)

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Population
servedN/ADistribution (m3/d)

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Servicecoverage(%)

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Pipe length (km)N/A

NRW (%)

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Number of staff

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Number ofwatersources
Water rates(JPY)

Summary

Current Status& Challenges

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(in case of 10m3 of water use per month forresidential customers)

In Japan, water supply service is available 24/7 to almost 100%1) of thepopulation. The number of pipeline incidents has been decreasing year byyear2) due to systematic mains renewal and regular leakage investigations. In
addition, customers are experiencing fewer large-scale service disruptions3)
or turbidity issues in drinking water owning to the development of dams.
Under these circumstances, there is a growing demand for even safer,higher-quality tap water, and many water utilities are conducting thoroughwater quality management at every stage from the source to tap.
This paper discusses how common water utilities in Japan prevent thegeneration of turbid water in the water distribution network.
In Japan, water mains installed during the rapid economic growth period
after the Second World War are facing the time for renewal, and water utilities
are implementing capital programs to renew their aged mains
systematically. After a new main is installed, its inside is cleaned to ensure thesafety of water quality. In addition to the planned construction work, systemswitch and pipe cleaning are also carried out to deal with sudden leakage
incidents.
When system switch and pipe cleaning are carried out, the direction andvelocity of the water flow in the distribution network may change, resulting
in turbulent flow. In places where the flow velocity is low, tiny foreign
substances contained in the tap water accumulate over a long period of time,
and turbid water is generated when these substances and the iron rust on theinner surface of unlined mains get rolled up by the turbulent flow created bysystem switch and pipe cleaning.
To minimize the generation of turbid water by system switch and pipecleaning due to pipe renewal and unexpected leakage incidents, it isimportant to formulate their work plans appropriately.
Efforts to deal with turbid water
1. Consideration of the range for turbid water
As mentioned earlier, turbid water may be generated when the flow
velocity and direction in the distribution network change. Therefore, whenplanning valve operations for system switch and pipe cleaning, a pipe network
calculation is normally performed to simulate potential changes in the flow
direction and velocity.
The calculation result shows you the degree of change before and after thevalve operations to help you determine the range where turbid water may begenerated. Table 1 shows the characteristics of the pipelines in which turbid
water may be generated.
Table 1 | Pipelines susceptible to turbid water••
Measures &Solutions•••

Pipelines containing aged pipes (unlined cast iron pipes)
Pipelines whose flow velocity largely changes before and after thesystem switch
Pipelines whose flow direction is reversed before and after the systemswitchPipelines in which water is stagnated
Pipelines located adjacent to the operated valves, etc.

2. Consideration of work hours
As shown in Figure 1, the flow rate in the distribution network varies
depending on the time. More specifically, the flow rate peaks in the morningand evening, while it becomes low at night (meaning low flow velocity).
Therefore, if the work hours can be selected, you can avoid generating turbid
water or to reduce its generation range by switching the system at night when
the flow velocity is low.
As a result of the pipe network calculation, if there is a concern that a
daytime work could generate turbid water, utilities make a comparison to see
when is the best time to conduct the work on that day to minimize the rangeof turbid water being generated.

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Distributed amountTime

Figure 1 | Fluctuation of distributed amount of water by time (example)
3. Consideration of pre-cleaning
Once turbidity substances get rolled up, they will move with the water flow
and affect a wide range of the distribution network. Therefore, when turbid
water is expected to be generated even if the work is done at night, utilities
limit the scope of turbid water to the mains to be cleaned by cleaning themin advance.
When utilities conduct the pre-cleaning, first, based on the result of thepipe network calculation, they identify the mains where turbid water isexpected to be generated, such as those whose flow velocity is expected toincrease largely, and get rid of the foreign substances out of those pipes using
the drainage facilities and fire hydrants on those mains. To obtain a sufficientcleaning effect, the flow velocity in the main must be 1.0 m/s or higher, orhigher than the maximum flow velocity that is normally attained.
During the cleaning process, the valves are normally shut off to prevent theturbid water from flowing into other mains than the ones to be cleaned. At
this time, it is also important to check the valves’ opening/closing statusproperly so as not to shut off the inlet valve of the customers who have asingle point of inflow because its shut-off would cause them disruption ofwater supply.
4. Public relations
If the occurrence of turbid water is still unavoidable after taking thesemeasures, advance notification to the public is necessary. Ways of notification
include a customer notification through the utility website and handout
distribution at their premises that gives information on the potential service
disruption or turbid water generation. Providing necessary information inadvance is helpful to obtain understanding from the customers on the utility’swork.

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Below is a detailed example of a preventive measure against turbid water
generation, in which a water pipe bridge on a primary main (Figure 2) isintentionally disrupted to repair a leakage.

Reservoir

Range inwhich
turbidwater may
begenerated

(1)
(6)

Leakage(7)DA(8) (a) (2)B(d) (9)(3) (b)C(10)(c) (4)
S(11)

S1(5)
A

LegendOpeningvalve
Closingvalve
Firehydrant
AirAvalve
Drainage
Sfacility

Figure 2 | Image of mains
The primary pipe is looped, and the water pipe bridge has a leak that needs
to be repaired.
During the repair, it is necessary to shut off the valves (6) and (7) located at
the front and rear of the pipe bridge, but when they are closed, the pipeline
will be non-looped.
A pipe network calculation under peak demand condition showed that theflow velocity in a wide range of pipes would be higher than the normal
velocity, and that turbid water would occur widely.
On the other hand, a pipe network calculation under night-time condition
showed that the flow velocity would be higher than the normal velocity onlyin the range shown in red. And no turbidity is expected to occur in the pipes
whose flow velocity is normal or lower than normal since their water isflowing without getting turbid every day during peak hours.
Fortunately, the amount of leakage was small and therefore the risk of
secondary damage was also small, so the utility decided to repair the leakage
at night. Before doing that, they planned a pre-cleaning and public notification
procedure as shown in Table 2.

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Table 2 | Pre-cleaning procedure
1. Shut off the branch mains to prevent turbidity substances entering from theprimary main.
Tighten valves (2) and (4) while cleaning them with fire hydrants (a) and (b).
(Note: Make sure that valves (8) and (10) are opened in advance)(Note: Valve (3) cannot be tightened, so the customer at B should be notified
of turbid water)
2. Tighten off the downstream portion of the primary main.
Tighten the valve (5) while flushing it with the air valve.
3. Clean the primary main.
Open the drain valve S1 and drain the water to flush the foreign substancesout of the main.

By taking these measures, it will be possible to address leaks while reducing
the range affected by turbid water.

Future plans

References

There is no end to mains renewal process, and efforts to minimize related
impact of turbid water on customers will stay important. In that regard, theadvancement of ICT such as mapping systems have a potential to make itpossible to take more effective measures to prevent turbidity issues byenabling centralized management of information required for maintenanceand management of facilities.
Source:1) Water supply statistics (Ministry of Health, Labour and Welfare).
https://www.mhlw.go.jp/stf/seisakunitsuite/bunya/topics/bukyoku/kenk
ou/suido/database/kihon/index.html
2) The number of incidents in water supply (Water Supply Hot News, Japan
Water Research Center).
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&
cad=rja&uact=8&ved=2ahUKEwjQpamtsTrAhUexYsBHah7Bi0QFjADegQIBBAB&url=http://www.jwrcnet.or.jp/hotnews/pdf/HotNews563.pdf&usg=AOvVaw0BvlATxjJURB0No
8gvNhoP
3) Effectiveness of dams during droughts (Ministry of Land, Infrastructure,
Transport and Tourism).
https://www.mlit.go.jp/river/bousai/main/saigai/kassui/dam_effect_ind
ex.html
References:
Guidelines for Management and Maintenance of Water Supply Facilities(Japan Waterways Association).
5 / 6http://www.jwwa.or.jp/syuppan/hakkou.html

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