I am a third year mechanical engineering student at the University of Sydney and I have to develop a water supply system for a ten story building with 2 apartments on each floor.
My questions are the following:

Q1) Does a standard solution exists?

Sylvan's reply: I would think you had better get a code book ..Mate I'm from New York (USA) and to answer it from NYC stand point I would figure the following. Flow rate would depend on the fixture Units (FU) needed. A FU is based on 7.48 gallons. A Flushometer would require much more GPM's than a tank and bowl. You would also have to size this piping besides the GPM required BUT you must take velocity into consideration as you certainly do not want to cause a premature piping failure due to erosion (normally no more than 8 FPS) as this could also cause hydraulic shock (water hammer) and noisy system. (You may want to contact the Copper Development Association for their recommendations.)

Geoff's reply: There is no standard solution when developing a water supply pipework system for a multi-storey building as there are a number of variable factors that will influence the pipework design.

A good starting point would be to refer to Australian Standard 3500 1.2:1998, pages 17-20.
This section deals with "Sizing of Water Services".

Q2) What standard flow rate has to be provided?

Sylvan's reply: There is NO standard flow rate. Each building has to be sized on its own merits.

Geoff's reply: Flow rates are also covered in AS 3500 1.2:1998.

Q3) What are the regular diameters of the piping system (of the trunk pipe and of the pipes in the apartment)?

Sylvan's reply: By "trunk line" I guess you mean the water main piping. Again the size of this pipe is predicated by the Number of fixtures.

Geoff's reply: The "trunk pipe diameters" and the apartment pipework may be determined according to the information contained in AS3500 1.2:1998.

Q4) How much pressure has to be provided?

Sylvan (answering Q4 & 5): When using a graph you also should show friction losses through pipe and fittings (developed length) & consider the height factor. For pressure if your talking just hydrostatic you take the constant .434 x the height. This will give you no flow conditions. To figure the pressure required to elevate the water you take 2.31 x the incoming pressure to give you the height this water can reach BUT you still have to read the manufactures specifications as per friction loss per fitting and Then you must add into this pressure the REQUIRED min. press for the device you are going to operate.

Geoff's reply: The minimum working head at the furthermost or most disadvantaged fixture or outlet shall be not less than 50kPa (5m head).

Q5) Are you able to supply a graph showing the water demand on an average day?

Geoff's reply: There is no graph available but the average water demand would be related to the number of consumers and the types of fixtures used.

Q6) What are the regular assumptions/considerations made when setting up a piping system?

Sylvan's reply: Never ASS U, ME as you make an ass of you and me ASSUME NOTHING plumbing is a science and each system has to be designed. This is not a one size fits all. You can design a system by figuring that only 75% of this system would be used at one and base your piping sizes to this factor.

Geoff's reply: Considerations would be as follows:

• Available water pressure in the main
• Loading units
• Probable simultaneous demand
• Pressure at outlets
• Head losses
• Velocity requirements

Ferrous or non ferrous, as a Master Plumber we are responsible for figuring expansion/contraction and provisions to protect the piping from undue stress? We have to install how water recirculation lines to keep stand by losses to a minimum.

People take Master Plumbers for granted, never realizing the schooling involved to be a REAL plumber.
This building you mentioned can be piped several ways.
   1 - pumps to a roof tank
   2 - Hydro pneumatic tanks in the basement
   3 - Pressure boosters.
   4 - street pressure to a few floors and pump/gravity to the other floors.

Pump Schematic Courtesy of Nossiter Pumps

Are you planning on using the roof tank for fire protection? If so how many gallons of reserve are you planning to have?
If you do opt to go with a roof tank did you take into consideration the weight of the water AND the total weight of the tank. This ALL must be thought about by the "plumber" At least in NYC.
The final responsibility is ours as we must check behind the engineers and architects.