Hi, this is my first post so be easy on me!

I have a 2007 RRS 2.7 d and the low coolant mesage has flashed on a couple of times now. It happened for the first time last week but then didn't show again till now. I'm taking the car in for a service at the dealers next Friday and didn't want to mix coolants could help it, so I wanted to wait. I rang the dealers and they said that if it's not leaking it should have enough in there to last till next Friday.

I've checked and it's doesn't seem to be leaking and does have some coolant in it. I'm told that I could add a cup of water to it and that should see me through, is that right?

Welcome
Seems your not alone and it's probably the bottle or sensor.
Have a look at this thread here  ON THE WAY: BMW F21 M140i
MERCEDES GL350 - Metallic Navy Blue w/Grey interior

GOING: BMW F31 335D MSport+ xDrive Touring
GONE: Land Rover Discovery 4 HSE - Stornaway Grey w/Black Interior (wish we'd kept it )
GONE: BMW F10 520D MSport - Carbon Black
GONE:MY12 RRS SDV6 HSE Sumatra/Ivory/Grand Black Privacy glass

Thank you Beancounter_74

Although I'm not sure if the senor has gone or not. The coolant in the tank looks to be just under / on the line of the min boarder.

One thing that is strange though is that when I checked there is coolant at the top of the bottle but it doesn't appear to have filtered down it looks stuck there. Does anyone know if that means anything?

Sorry, I'm the last person to talk about 'technical' things, but hopefully someone will jump in here and answer for you.
Seems that the earlier models had a fault with the coolant bottles anyway, so could be worth sorting out for your own piece of mind  ON THE WAY: BMW F21 M140i
MERCEDES GL350 - Metallic Navy Blue w/Grey interior

GOING: BMW F31 335D MSport+ xDrive Touring
GONE: Land Rover Discovery 4 HSE - Stornaway Grey w/Black Interior (wish we'd kept it )
GONE: BMW F10 520D MSport - Carbon Black
GONE:MY12 RRS SDV6 HSE Sumatra/Ivory/Grand Black Privacy glass

I have exactly the same problem with mine. The coolant level was low and looked like some had congealed at the top of the reservoir. It's in being checked as I type ill let you know  RRS Dynamic

The floating foam ball sensor becomes porous and starts to sink causing false readings.