National Diploma Mechanical and Electrical Services Construction Cold Water Supplies

Mechanical and Electrical Services Construction Aims – To understand the process of providing Potable water to buildings. Objectives To understand how Water is collected. To investigate the Treatment process. To explore the supply and distribution of water in Urban Areas.

Mechanical and Electrical Services Construction It is estimated that every person in Britain uses 150 litres of water per day. Population figures for mid 2008 revealed that there is now 61,383,000 people living in the United Kingdom. By doing a simple maths calculation we can see this country uses a staggering, 9,207,450,000 billion litres of water per person per day.

Mechanical and Electrical Services Construction If we look at individual statistics for England, Scotland, Wales and Ireland. (Population figures supplied by the Office for National Statistics Population (mid 2008) Water Usage England51,446,0007,716,900,000 Scotland5,169,000775,350,000 Wales2,993,000448,950,000 Ireland1,775,000266,250,000 Totals61,383,0009,207,450,000

Mechanical and Electrical Services Construction The Primary source of water in this country is Rain. The Average annual rainfall in this country varies between 750 and 1000 millimetres, 30 – 40 inches ( Map.htm, accessed 19/02/2010) Map.htm In some parts of the world, countries with very low rainfall have turned to desalination of seawater to provide potable water. Potable - fit to drink.

Mechanical and Electrical Services Construction This rainwater falls into streams and rivers, and eventually ends up in lakes and reservoirs. Countries need to manage or harvest this rainwater, so that we have something to drink. So a lot of rivers have had a dam constructed on it to be able to provide us with adequate supplies of drinking water. A good example of this can be seen at the Brennig and Alwyn Reservoirs. ( attractions/Lakes_and_Reservoirs.htm )

Mechanical and Electrical Services Construction Rain that falls on the ground can also seep through the ground and into the underground water table. This water often emerges as a spring. It is also possible for us to drill into this water table and extract water in the form of wells.

Mechanical and Electrical Services Construction For water to be potable i.e. fit to drink, it must go through a process of treatment. It should be free from harmful impurities Any water collected from either above or below ground is likely to be contaminated. It therefore needs to pass through a treatment process.

Mechanical and Electrical Services Construction ScreeningSedimentationFiltration Sterilisation Untreated Water AerationSoftening Potable Water

Mechanical and Electrical Services Construction Typical water treatment process from Rivers or Reservoirs

Mechanical and Electrical Services Construction The cheapest and easiest way to distribute water is by gravity. The efficiency of a gravity fed system is dependent on the number of properties and the volume of water being supplied. This in turn is dependent on Pressure of water in the mains Size of the main Demand upon the main.

Mechanical and Electrical Services Construction Pressure of water is often referred to as head. Head – The height to which water in the main would rise in a vertical pipe. A suitable pressure, or a sufficient head of water, is considered to be 30 to 70m. This will allow sufficient pressure for all properties. Will also be acceptable for the Local Fire Brigade. Pipework would also be within normal strength requirements Transmission noise would also be limited to an acceptable level.

Mechanical and Electrical Services Construction Typical distribution of water from Water Towers and service reservoirs

Mechanical and Electrical Services Construction Water Pressure. The Higher a column or head of water, the more pressure is exerted at its lowest point. To try and explain this a little clearer we can use simple calculations. For example if we had a container that was 1m³ it would weigh 1000kg or 1 tonne. The force or pressure that this would exert could be calculated using the formula Force = Mass x acceleration. Force = 1000 x 9.81 Force = 9810 Newtons or 9.81 kn/m²

Mechanical and Electrical Services Construction So if a container 1 metre high exerts a pressure of 9.81 kn/m² Then a container 5 metres high would exert 5 times the amount of pressure. 5 x 9.81 = kn/m2 1m 5m

Mechanical and Electrical Services Construction What we have just calculated is known as the Intensity of Pressure. We can now use this Intensity of pressure to calculate the head of water in a given system. For example. If the mains water pressure is 450 kn/m², calculate the head of water. The formula we need for this is Intensity of pressure = Head x 9.81 By transposing the formula for Head. Head = 450 ÷ 9.81 Head of water = 45.87m In other words the water would rise metres in a vertical pipe.

Mechanical and Electrical Services Construction Water is distributed from water tanks / service reservoirs by means of a water mains. Trunk mains are used to carry large volumes of water into built up areas. These are then reduced into street mains and finally a sub mains before entering a building.

Mechanical and Electrical Services Construction Typical water distribution to buildings

Mechanical and Electrical Services Construction Water supplies are now connected to individual properties. However the Connection must comply with the Water Supply (Water Fittings) Regulations And any Water Bylaw requirements. All new properties will now be fitted with a water meter and a stop valve. Both of these will be situated on the local authorities land.

Mechanical and Electrical Services Construction

The local authority stop valve is usually sunk in the ground to a depth of between 750 and 1000 mm. And is encased in brickwork, concrete or a stoneware pipe allowing for easy access should the water need to be shut off. From this stop valve a smaller pipe known as the service pipe is fitted which brings water into the house and is known as the rising main. The position of the service pipe should be to negate the effects of frost, any heavy traffic or any building loads

Mechanical and Electrical Services Construction The most common place for water to enter a house is under the kitchen sink. Where ever the service pipe enters the house, it must be housed in a protective duct, which is suitably sealed and insulated. This will enable a new pipe to be fitted if necessary. Once inside the building another stop valve and a drain down facility will be fitted. From here a branch may be taken to the kitchen sink, otherwise the rising main will run to a cold water storage tank or cistern, usually located in the attic or roof space.