So far:
* increase maintenance (and building) costs for pipes.
* introduce random pipe breaks
-could cause local minor floods and the need for repairs, until then blocking traffic
* a new service building required for water that is required for maintenance.
-pump stations, may serve a certain radius of area to keep the water pressure in appropriate levels, so you actually would have to consider where to place them strategically best, also considering running costs and(!) electricity consumption
*new buildings to add taste to the overall water network (all including considerable building and maintenance costs and also electricity)
- water cleaning facility (a.k.a. treatment plant), filtering dump water, then releasing it down into the ground water
- water works, conveys fresh water from the ground water
Adding to this discussion, the main "problem" with the way CS deals with water/sewage systems is that, as many of you already said, they don't have an impact on gameplay.
Right now you either supply water/sewage to RCI buildings and they develop normally or you don't supply it and they "get out of town".
In SC4 there was actually a gameplay reason to lay pipes. they would allow RCI buildings to grow beyond the lowest density and wealth levels. You could still build a city without water if you wanted to have a low density and low wealth urban feeling.
In some of the cities I currently have in my SC4 regions I'm actually building water pipes only in small specific areas of the city to keep the water consumption just below the capacity of the water tower since I'm trying to build cities following some principles of "organic growth". All this adds a level of "role-playing" to the game.
A similar approach could be possible for CS in which RCI buildings without water would not grow beyond level 1, as someone already suggested.
However, the best approach to the water system ever made in any SimCity game is, in my opinion, the way SC 2000 deals with it.
Brief explanation of the system:
- RCI buildings have small pipes under them and you have to connect "main" pipes to those small pipes to supply water/sewage to the buildings;
- RCI buildings without water don't grow beyond the lowest density level;
- Seasons and weather affects the consumption/production of water;
- Water towers don't pump water, they store excess water to be used in case there's a situation that causes the water consumption being higher than the what production rate (like a drought or the arrival of summer).
The fact that the player also needs to account for the storage capacity and the effects related to the "weather and seasons" presents the players with an more interesting set of mechanics for the water system.
This also makes it so that the amounts of water being produced and consumed are dynamic, which gives the player a reason to periodically check the status of the system and account for weather effects like:
- drought - decreases the production rate of water pumping/desalanization facilities;
- forest fires - sudden increase in water consumption level;
- floods - increases the production rate of water pumping/desalanization facilities and increases risk of suffering a flood disaster;
- etc.
This elements help to create a system where the player has to keep checking how things are going and has to periodically modify the system to meet the demands of a growing city while trying to account for possible emergency events and keeping the budget under control.