"We have bread and water."
Translation:Mamy chleb i wodę.
because it is not correct in Polish.
correct declension form is "(my) mamy".
If you have heard this kind of structure from some Polish people- it is a regional dialect, not standard Polish.
Does it make any difference if you put the pronoun or not when speaking? What is the common way ?
Usually you don't, it's pretty redundant. The form of the verb makes it obvious who the subject is, and with 3rd person you will rather use something more specific (my boss / Anna / George's sisters) than he/she/they. Also, in real conversation you will have context.
You rather only use pronouns when you need to emphasize something or contrast it with something else.