I am looking for different opinions on the material and thickness (pressure class) used for water mains and sewer force mains.  There is usually a local utility standard that I have to meet, but in this case the local utility has no established standards.

In the absence of any local standard or special considerations, assuming you are in the US, what type of material and pressure class would you use and why for a force main and water main?

We have a 2 1/2 mile long force main with a gravity discharge.  There are no other connections to the force main, although there may be connections in the future.  Maximum working pressure is less than 50 psi.  Size is 12" diameter. 
The water main is a grid pattern on a 400 acre mixed use development.  Maximum working pressure is 75 psi.  Sizes range from 8" to 16" diameters with some short 6" stubs for fire hydrants.  There are fire hydrants on the lines, but no fire department connections, as these would be on the individual parcels. 
The topography is generally flat.  Freezing temperatures are not a consideration.

I would appreciate any opinions on materials and pressure class for this situation.  In the absence of local standards I used the design standards of a nearby utility whose manual and specifications appear to be the most thought out.  I would also appreciate any thoughts about whether there is an industry standard.  I have worked with about 5 local standards, and they all have slight differences in materials and pressure class for water and force mains.

The reviewing authority has the ultimate determination on piping materials. That would probably be the State where your project is located.

Here is a typical specification:

All material including pipe, fittings, valves(Bellow Seal Valves), and fire hydrants shall conform to the latest standards by the AWWA and ANSI/NSF, where such standards exist, and shall be acceptable to the reviewing authority.

In the absence of such standards, materials meeting applicable product standards and acceptable to the reviewing authority may be selected.

The reviewing authority has the ultimate determination on piping materials. That would probably be the State where your project is located.

Here is a typical specification:

All material including pipe, fittings, valves, and fire hydrants shall conform to the latest standards by the AWWA and ANSI/NSF, where such standards exist, and shall be acceptable to the reviewing authority.

In the absence of such standards, materials meeting applicable product standards and acceptable to the reviewing authority may be selected.

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