Researching the IC mainline here in South Central Illinois I’ve discovered that the railroads in this part of the country often built a reservior and pump house to supply their trackside water towers. Anyone modeling this detail?
You mean like this one:
It’s on the UP about 30 miles west of Twin Falls, ID.
Here’s my model (from a Campbell kit):
I’ll be placing it next to the water tower in my little town of Butte Creek, OR.
Exactly. I look at a lot of layout picture and I don’t often see the pump house or the reservior (lake) that the railroad often built to hold water to be pumped into the tower. There are two lakes within 5 miles of my home that were originally built by the railroad to supply water.
I like to model water supply and fire protection systems for my saw mill and other areas. I use a combination of gravity tanks, steam pumps and suction tanks. In the photo below, a pump house takes suction from a river below and pumps the water through a 6 inch pipe along the bottom of the bridge to a suction tank on the other side of the river. The track across the the bridge is dual gauge and forms a bottle neck as you can see the 30inch gauge steam locomotive awaiting it’s turn as a standard gauge Shay takes suction via a steam siphon on the other side. 
Peter Smith, Memphis
All of my water towers have pumphouses, either like the small one shown here, for towers with spouts:
…or like this, in the tower support, for supplying multiple standpipes:
This powerhouse, at left, supplies electricity, water, steam and air to the nearby shop complex, and also water to the standpipe in the following picture:
Wayne
The gravity tank on the hill supplies the standpipe ( Seen just above the red sand house roof). It also supplies the water tank in the foreground. The boiler house to the right provides heat to the sand house. 
The gravity tank in this photo provides emergency water to the boilers in the boiler house. It is supplied from the main mill steam fire pump located in the mill power house. This pump also provides fire service water to the mill sprinkler system. The red dry pipe sprinkler system valve and piping supplying protection to the flammable liquids shed can be seen seen to the right. 
Peter Smith, Memphis
These photos show the tower, pump house and the edge of a larger storage tank. If memory serves I believe there were two of the larger storage tanks and also a pipe suspended in the air running from the hill in the background. There were also the remains of a turntable nearby. Brent 
Since the area where my prototype ran had vertical scenery, all that was necessary was to put a small diversion dam on a watercourse uphill from the standpipe and make sure the piping could handle the pressure and volume. The only water tower will be one for municipal drinking water at my one fair-size town.
I agree that places in the flatlands would have to have pump houses and such. There just aren’t any such places in the Tomikawa Valley.
Chuck (Modeling Central Japan in September, 1964)
Speaking of vertical scenery, below is a picture I took along the Cass Scenic Railroad in West Virginia while our Shay was taking on water during our climb up 11% grades. The water tank was located along a mountain stream which filled the tank and then overflowed back into the downstream side of the stream. The Shay was using a siphon to take on water. I borrowed this scene in one of my previous model photos but used a pump to through put the water through the tank. 
Peter Smith, Memphis
Brass water tank with a Showcase Miniatures “pump house” kit that are both Southern Pacific RR in design. 