Unit 205: Cold water systems
Outcome 2
Requirements of the cold water
supplies into domestic
dwellings
Requirements
Incoming mains Service pipe
Mains 25mm MDPE
Ferrule/isolation (min)
Meter/isolation Ducted
Communication pipe Rising main
750-1,350mm 15mm (min)
deep Stop valve
15mm (min) DOV
Stop valve
DOV
Requirements
Water meters
Internal and external meters
Internal
meter
needs to
be cross A boundary
bonded meter box
for safety
Requirements
• MDPE pipe is blue to identify wholesome water
• Minimum size to modern property is 25mm
• Soft copper can be used (R220)
• Meter is commonly installed at the property boundary
in a chamber (protection, frost, reading)
• Some meters are internal and installed to rising main
• Water can be isolated in the road, at the meter, or at
the point of entry to the property
Everything from the external stop valve at the meter is
regulated under the Water Regulations 1999.
Requirements
The Water Regulations state:
As far as reasonably practicable, a stop valve should be
located inside the building, above floor level, as near as
possible to the point of entry. It should be installed so, when
closed, will prevent water going to any point in the building.
Water undertakers recommend no more than 150mm of
MDPE is above floor level (it degrades in sunlight). Either
a screwdown (BS1010) or a level arm (BS6675) stop valve
can be used.
Requirements
The stop valve works by the handle being turned. This in
turn screws down a jumper with a washer attached. This
washer is pushed against a seating to create a watertight
seal. If the valve jams, a cost effective method
of repair is to replace the head gear only.
The DOV works using a spanner or key on
the square drive. This in turn screws down
a jumper and washer onto a seating, to
create the watertight seal. A DOV must
be installed above the incoming stop valve
and at every low point in the system.
Requirements
• Plumbing system must comply with the Water
Regulations
• Every plumber must prevent contamination of
wholesome water
• Advance notice must be given of installations
• Benefit from becoming an Approved Plumbing
Contractor, after passing the Water Regulations
training course
• WRAS has produced the guide to the Water
Regulations, which is the essential guide for plumbers
Requirements
Two key tests with cold water systems:
• Pressure
• Flow rate
Pressure is normally
first tested near to the Flow rate is tested
point of entry at each outlet
Requirements
Pressure
Pressure refers to the force behind water flow. Normally,
in domestic situations, a visual check is suffice but when
installing certain appliances, a more accurate reading
needs to be taken – water softeners, combination boilers,
un-vented cylinders, or if pipework is being altered
dramatically.
Pressure in plumbing systems can be created by two basic
means: either a pump can be fitted (mains water is also
pumped water), or pressure can be created by the weight
of water – the head.
Requirements
Flow rate
This is the volume of water discharging to an appliance,
and is measured in litres per minute. So, if the flow rate
was poor, the bath would take longer to fill up.
Normally, in a domestic situation, a visual check would
suffice but you can always check by using a flow cup or
weir cup (this would be critical when setting up a
combination boiler or monitoring an unvented cylinder).
60 litres/min = 1l/sec
6 litres/min = 0.1l/sec
Requirements
Pressure and flow
These can be effected by:
• Daily demand (peak periods)
• Location
• Age of property
• Distribution main size
• Incoming main size
• Installation pipe size
• Materials used
• Number of elbows etc
• Blockages
Requirements
Direct system
This is a cold water system where all the cold water in
the property is supplied directly to each outlet on mains
pressure – high pressure.
The size of service pipe to the house is usually 25mm
MDPE, which is connected to 15mm copper in the house.
Old houses may have 20mm MDPE copper or lead mains.
On a direct system, it is important to take precautions
against backflow.
Requirements
Direct system
This is a cold water system
where all the cold water in the
property is supplied directly on
top of each outlet on mains
pressure – high pressure.
Direct system
The only stored
water is for the hot
water system via
the cylinder.
Only one DOV is
required to drain
the system down.
All pipework can be
15mm due to the
system being high
pressure.
Requirements
Direct system
Another direct system is
when a combination boiler
is used, and both hot and
cold are directly off mains.
In this case, there is not
stored water at all.
An unvented or water jacket
heater hot water system
would be the same.
Requirements
Direct system
Advantages:
• Potable water at every draw off point
• Good pressure at all draw off points
• No concerns about storage cisterns in lofts
Disadvantages:
• If the mains is turned off you are without water
• Pressure varies during the day and at peak times
pressure can be very low (6.30–8.30am and 5–7pm)
• Care when fitting showers/mixer taps
Requirements
Indirect system
This is a cold water system in which the cold water is taken
via the rising main to a high-level storage cistern. From
there, most of the cold water outlets are fed – low
pressure – except the kitchen sink, which is mains-fed to
supply wholesome water.
The distribution pipe from
the storage cistern needs
to be either 22mm or
28mm, and reduces in
size as appliances are fed.
Requirements
Indirect system
A low pressure system feeding most outlets in the property.
Requirements
Indirect system
Advantages:
• Stored supply of hot water, should mains be turned
off
• The system pressure is unaffected by peak time
demand (constant pressure)
Disadvantages:
• More pipework in roof space – risk of freezing
• Possible contamination of water at draw-off points –
storage cistern
• Only one draw-off point gives potable water
• More expensive
Requirements
Cold water storage
If a cold water storage cistern is required, both BS6700 and
the Water Regulations outline:
If supplying either hot or cold – 100-150lts
If supplying both hot and cold – 230-250lts
By inspecting the loft to see the CWSC, or by testing the
outlets, the system can be identified.
City and Guilds 6035
Level 2 Unit 205
Requirements
Rainwater harvesting
This can save a
householder large
volumes of mains water
and reduce the pressure
on this resource.
These storage cisterns
are installed below
ground and collect water
from gullies. The average
size may be 5,000 litres.
Requirements
Grey water recycling
This system collects
waste water from baths,
showers and washing
machines. It is commonly
used to flush WCs.
Requirements
• With both rainwater and grey water, it is important to
prevent contamination of wholesome water
• These systems must be independent
• Pipework must be identified properly
• These systems are easier to install on new builds
rather than retro-fit
• These also help with the increasing green demands
of society
Requirements
To identify which system is installed in a property the
plumber could:
• Take a pressure reading at various outlets
• Go up in the loft and identify the cistern sizes
• Turn off the incoming mains and identify the outlets
that stop flowing
An important factor is, whichever system is installed, the
outlet has sufficient pressure and flow for the appliance.
