Taken from "Sheep Raising 101"
Early Weaning
Early weaning is a relative term, but implies weaning at any time after 21 days of age, but usually before 90 days. 60 days is a common weaning age in intensively managed sheep operations. Early weaning can be successful provided lambs are drinking...
4 weeks isn't old enough to wean. Sheep are very similar to goats, you need to wait until 8 weeks at the very least to wean them. They should still be getting milk, not just water.
After that, do not give them water in a bottle, that is counterproductive to your intent. Instead, try...