The ideas are:
1)
Hydroelectric engine
Crafting
R N R
where
R is a rotor
N is nothing
How it works
Imagine such a construction:
S
F
F
F
F H
(S - Source water block, H - engine, F - flowing water).
The engine here produces 4 EU/t since the height of the waterfall is 4.
The Hydroelectric engine can't be forced in producing more than 5 EU/t (to fit in ULV range and also prevent them from being OP). If this happens, the engine will explode.
2)
Compact WaterMill engines
The compact engines will not use flowing water. Instead, water will be sent to the engines via pumps.
Important information
When water is being carried with a fully loaded Gold Waterproof Pipe I'll say that the rate is 1 WU (Water Unit)/t (I don't remember how much is this in millibuckets).
Also, the water is supplied not to the engine itself but to the Stationary Rotor located directly below the engine. The crafting recipe is:
R N R
N M N
R N R
where R is a rotor, M is an advanced machine block, N is nothing
Devices
The 1st device is the ULV WaterMill engine. It accepts 1 WU/t and outputs 4 EU/t.
The 2nd device is the LV WaterMill. It accepts 4 WU/t and outputs 32 EU/t.
The MV WaterMill accepts 16 WU/t and outputs 128 EU/t; the HV one accepts 64 WU/t and outputs 512 EU/t.
To make the 2 latter watermills accept so many WU/t a Water Compressor is used. It turns water into Compressed Water for a ratio of 16:1. It should be able to accept
both pump input and manual one. Compressed water should have a navy colour.
Crafting
The ULV engine is shapeless crafted out of the Hydroelectric engine and backwards.
The higher tier engines are crafted in such a way:
N W N
W T W
N W N
(where W is a lower-tier mill, T is a transformer upgrade).
P.S. If the author explicitly states his or her unwillingness to make such devices, I will create a thread in the Addon Request/Suggestion forum and move this entire post there.