How much water pressure loss in one drinking water pipe fitting? E.g Elbow

I don't know the questionneir is an Engineer or not, however this is for general information that Elbows, Tees, valves etc are the signiuficant component of piping system in which pressure drops occurs. But before that we must know the material and types of pipes. The losses can be calculatedeasily by equivalent length method( L/D ), which is a rough calculation method.

This method may be defined as the pressure drop through the fitting is equivalent to the pressure lost through a certain length of piping at that crresponding flow rate. But most accurate way to use this method is when tabulated data is available for fitting at the given size, roughness and turbulant number(Re). By the experiment, if the equivalent length for a range of sizes of a given type of fitting( Elbow, Bend etc.) are divided by the diameter of the fittings then a constant ratio (Le/D) is obtained. This value is very significant and makes the tabulation of equivalent length data very easy, becausse this single data value is sufficient to cover all sizes of that fittings. For example, Le/D value of a 45 degree screwed elbow is 13.

However this approach does not consider turbulence and subsequent losses caused by different velocities.

There are ready to use tables for each size of pipe. Try NFPA 13 for this cause.

The thing about pressure drop in fittings is that all methods used are approximate as the friciton factor or c coefficients used in hazen williams equaiton is only a rough approximation as a result of series of experimentation.... funny thing is if we look closely the friciton factor is not even a constant it varies through the length of pipe/fittings, but anyway for engineering applications its fine to consider it constant for a one matrial against one fluid which in your case is water, equivalent fitting method is commonly used (Carrier HVAC Design book) or a seemingly more accurate method yet less commonly used is given in ASHRAE fundamentals which uses some constants and multiplication factors which all amounts to experimental results and careful approximations....... 

There are two methods 1)equivalent length method in which each fitting is designated with equivalent pipe length and 2) K factor loos this is based on the reynolds number for each fitting according to its diameter and length.

Which ever suits you that can be adapted how ever k factor method is accurate and precise and equivalent length method is rough.

Refer to ashrae for chilled water and upc for water supply or drianage

The amount of water pressure lost in one drinking water pipe line is more than 24 bar

I think it`s the critiria to take advantage of AWWA.  And  full used of it.

its depent on pipe size types of pipe plastic, copper and etc. each fittings have different loss as per Plumbing Engineering Services Design Guide IOP 2002