water flowing out of the tap into "atmosphere" cannot be done with flow simulation. you'll need to look at another package.
you could model the tap and have an environmental pressure condition at the end and look at the internals to the tap, but you wouldn't know how it exits. and the exit would be much simplified compare to what actually happens.
you could extend a box around the tap as if it is submerged in water and put environmental conditions at the top of the box and do some really rudimentary tests but i don't think it would accurately match what is happening.