Thiazides in Diabetes insipidus. How do they reduce urine output?

Diabetes insipidus patients have diuresis due to ADH deficiency. To treat that, one of the drugs used are thiazide group of diuretics. How is that a diuretic is used to 'treat' diuresis?

Thank you very much, I have understood this now. Your writing style is very clear and helps me in understanding easily. Keep it up...

Thanks very much. Much appreciated response.

hello. i'm a portuguese med student. (so, first of all, i'm sorry for the bad english)
i was looking in the net, because i have the same doubt.
and i'm not really sure that i've understood your awnser...
As you explained here, thiazides will always have antidiurettic efect...!
every time that thiazides were taken, there would be "increased renal sodium excretion. This sodium loss causes extracellular volume contraction, resulting in reduced GFR and increased sodium and water reabsorption at the proximal tubule. Hence, less sodium and water are delivered to the distal tubule and collecting duct and less of these are lost in urine"

and that's not the case... most of the times, thiazides have diurettic effects, don't they?
why is it different in the case of diabetes insipidus?

Isn't more probable that thiazides, somehow, have some effect in one step of que reactions (adenil ciclase, stimulating PKA..) that expose aquaporines to the apical membrane?