While 90KKm may not seem like much, my 07 N52 (530i) pump failed at 100KKm (60Kmiles). Identical symptoms to yours.
My other 07 N52 (a 328Xit) pump showed symptoms around 105K miles.
The Pierburg pump failure mileage seems to be sooner on some early N52's, and better on later -- yours is an early N52. But failure is random, though usually after 50K miles.
The electronic pump (AFAIK) was first used by BMW on the N52 (and N51, I suppose) after exclusively using mechanical ones.
Bottom line is (1) it's not at all unusual; (2) it can't be fixed and must be replaced asap before it strands you and (3) DIY is about US$350-400, and US indy is US$ 800-1000.
If it fails on the road DO NOT drive the car -- not even a couple of KM. Flatbed it to repair location.
On a RWD, it's a fiddly but straightforward fix. On the AWD it's much more if a pain in the ass, since it feels like they built the frame around it. But it's doable, with patience. Most replace the thermostat at the same time, since they both have to come out. Kits available at FCPEuro and others.
Thanks for the thorough response.
90k km's (90,000 km's) which I am reading is about when pumps fail for people. Hopefully that means the valve is fine too.
Never used tap water in it. Just distilled and coolant fluid (if I remember correctly, definitely it was a coolant fluid people on forums said was the right and best kind). I'll check the fuse and look at the manual today, but it's probably the pump.
Other forums have said to replace the thermometer with the pump so I'll do just that.
Cheers