Here is a section that I took out of Urban Development because I felt it got too detailed. Urban Development is intended to generate a 10,000’ foot view of the town or city (or village) and not get into all the minutia. However, I think the questions are still valid.
So let’s go straight to water. A community needs water for drinking, for cleaning, and for irrigation. They may also need water for power. It’s not really reasonable to figure out how much water people or crops need, but you can work on how they get the water to where they need it.
If a river runs through or past the town, how do the people get that water to their homes? If this is a large city, chances are they aren’t all using the main river. Are they using smaller streams that feed into the river? If so, you’ll want to start drawing those in on your map. The location of the creek is probably less important than the way it is going to affect the roads and bridges.
If you’re going to have the fields irrigated, how do you want it to work? What’s the technology level or magical ability of this place? Do you want to have an Archimedes' screw? a shaduf? a water elemental? buckets on ropes with donkey power? aqueducts? Possibly more important, would they have dammed a river or stream and redirected it? Maybe the irrigation of fields is controlled by the dam and not by a more manual movement of water. If it is a dam, who controls the dam? A local merchant? the farmers? most likely the government. Again, it is less about the amount of water (because you likely already said there was enough) and more about how the water moves from one place to another.
For the record - Brinston, my biggest city, uses a variety of methods. They have deep wells that have hand pumps to bring the water to a cistern. They have a dam that directs water either into the nearby river or into the city, and if into the city, into the nobles’ quarter or the military quarter. The water travels through canals, not necessarily aqueducts. Plus they have a major river. Now most of the city is up on the cliffs. Only the fishermen live down by the river. This means the fishermen can get their water directly from the river, at least some of them. Some of the fishermen are too close to the sea and the river is brackish near them. They have to cart their barrels upriver to where the water is more drinkable and fill up there. Then again, the river is cleaner during low tide, so the fishermen might not be fishing then anyway (depending on when they got out in their boats).
Rhum has wells. The wells either work on rope and bucket (with a winch most often) or on a type of Archimedes’ screw that brings the water up to a “fountain”.