Morning BMX,
I think i can answer your question regarding the black deposits you're getting in your taps and shower head.
Working for a water company, I visit customers who call with this type of query quite often.
From what your are describing, the black slime is something called "Geletanious growth". I plain english its a build up of non-harmful bacteria.
The ideal conditions for bacteria to grow are somewhere damp and warm..... and your bathroom is the perfect place to find both these conditions. After using your taps/shower, the inside of the taps/showerhead will obviously be damp and the room wil stay warm, and the bacteria think its time to breed. The first you know about it is when enough has grown and the flow of water dislodges the colony which you see come out of your tap as a black slimey deposit.
Don't worry though as this is easily sorted.
If you go and buy a decent mildew cleaner, the shower head can be soaked in, more than likely it will dismantle for easy cleaning.
Depending on what type of taps you you have depicts the method of cleaning them.
If they are old taps where you have no sprinkler in the outlet, you can get a small bottle brush, soak it in the mildew cleaner and give the taps a good scrub, then flush then both out buy running them at full flow for a couple of minutes.
If they have sprinklers in the end, these can be removed, normally by inserting a screw in the middle and pulling down with a pair of pliers, then clean as described above. Don't forget to clean the sprinkler as well.
Should you not fancy taking the sprinkler out, just find some way of squirting the mildew cleaner up into the tap and let it sit there for 10-15 minutes, then run your taps again on full flow to flush the deposits out. This may be worth doing 2-3 times for the first time, then clean once every 1-2 months after that.
Hope this helps, and I haven't sent you to sleep