Until water was plumbed in houses, water gathering was a tedious and hard manual task usually assigned to women. Caroline Davidson, in her excellent book, A Woman’s Work is Never Done: A History of Housework in the British Isles 1650-1950 gives, in Chapter I, entitled “Water a truly awe-inspiring account of women in England gathering water from local pumps or streams, during the 18th century.

It was considered a woman’s task and was arduous. Rainwater was also collected in butts, but often there was not enough to hand for domestic chores and washing. Homes without piped supplies also had additional problems of the removal of dirty water. This task often fell to women too.

Note that water was rarely available directly in an eighteenth century kitchen.

Chistina Hardyment’s very useful book Behind the Scenes: Domestic Arrangements in historic Houses explains why ;

The scullery was originally the realm of the escullier, or cupbearer, and it was here, rather than in the kitchen itself that plates, jugs and kitchenware of all sorts were originally kept.

The scullery’s most important function was washing up and its essential furniture was one or more sinks, so the escullier evidently had to wash up cups as well as to bear them.

It was unusual, until the twentieth century, to have a sink of any sort in the kitchen itself. Even in very small dwellings, waterworks were kept strictly separate from the main cooking hearth, and it was a matter of principle to separate the washing of dirty things from the cooking of clean ones.

This was originally a practical measure: the first sinks were basic and leaky, and the floor beneath them was likely to be lethally slippery. Moreover, kitchens with open hearths produced so much dust and heat that anything stored there would have become somewhat grimy. In the small room at the base of the tower flanking the great kitchen at Compton Castle, there are traces of drains which suggest that it was once a scullery, and at Cotehele a small room with a sink is tucked away behind the kitchen.

Shallow earthenware sinks were mass produced in the Midlands from the eighteenth century. The materials a sink was made of depended on what was available locally slate and granite lasted best; sandstone was kindest to the crockery. Wooden sinks lined with beaten lead or copper were popular though expensive and liable to leaks.

Besides being used for washing up, the scullery was “the proper place for cleaning and preparing fish, vegetables etc., and generally for processes in connection with cooking which entail dirt or litter, and should therefore be kept out of the kitchen” (Our Homes). Loudon recommended at least two sinks, a board for dirty dishes and plate rack for drying. ‘There might also be a fireplace, a small brick oven and a large oven if the bread be baked there,’ he added; ‘coppers for heating water for the use of the kitchen-maid, dressers and tables, shelves for saucepans, etc.; and it should be well supplied with water.’ The floor needed to be easily washable, either stone or tiles, but preferably with a drain at one corner so that it could be swilled down on occasion. If convenient, it should open into the kitchen court so that access could be had to coal, wood and the ash pit. The scullery at Calke has a lead-lined chute through which edible scraps could be thrown into the pigs’ mashtub which was kept outside. 
Page 166

Here are two descriptions of rather grand sculleries, from the same book:

In a mansion like Dyrham Park, which was rebuilt in the 1690s, the scullery was dignified with the name of ‘little kitchen’, and kitchen tasks were divided between the two kitchens and a pastry. The 1710 inventory shows that both food preparation and cooking was done in the ‘little kitchen’, which was in the charge of the ‘Skullery Housekeeper’. Only a ‘copper boiler’ and a ‘great grate’ with a jack and a chimney crane are mentioned in the ‘great kitchen’.

and

Saltram boasts a roomy scullery, built with the new kitchen in the 1780s. Its splendid sinks, one of porcelain, the other of wood with a copper lining hammered over it, probably date from a hundred years or so later on. There are two large coppers, still impressively well-polished, used for boiling vegetables, puddings and hams, with fine tight-fitting copper lids. Hot-water cans are lined up on a shelf, to be filled morning and evening from the hot-water boiler at the back of the kitchen range. A scullery on this scale could be, and evidently often was, used instead of the kitchen when only a small amount of cooking was required, or if the family was absent. 
(Page 168)

On a side note, you might like to know that the water pump which fed water into Steventon Rectory is the only remnant of Jane Austen’s childhood home which still stands.