The water source for some of the bees is a very dilute sugar solution (probably weaker than Skyhook's Dad's bee book of the 1930s).
Of course it has to be the Dartington, so an entrance feeder is acually within the hive entrance - just tucked under the front 'sealing dummy' (while there is still space, as I added another frame of foundation at the front of the broodnest yesterday).
I have just looked at another with an entrance feeder (with very dilute sugar solution) and I see that is empty, So I expect the dartington will be depleted too.
I am more convinced than ever that it is just a continuous supply of water they need, not the sugar, for the boost in spring development. After all there are copious amounts of honey still in the hives. Them using water to dilute it, for larval food, will allow more space to be freed-up for brooding, too.
The rest make their own arrangents for water collection - a shallow plastic tray filled near to brimming with water and soggy woodshavings is presently a favourite. The sources are about ten metres from the hives.
Regards, RAB