Water
The water on my layout was done with a low odor two-part polymer coating manufactured by EnviroTex. Although relatively expensive, the advantage of minimal obnoxious odours is worth the extra cost as long as you are not doing very large areas.
The creek bed is prepared by finishing the edges of the embankments with rock castings and rubble. The creek bed was floated with very thin plaster and allowed to dry thoroughly. The rocks and creek bed was painted and finished before application of the EnviroTex. Shale was spread across the bottom of the creekbed and up the sides above the intended waterline. Twigs, branches and other detail items such as discarded tires and lumber are added and held in place with a liberal coating of white glue.
The EnviroTex comes in two containers, one being the resin and the other being the hardener. Equal amounts of each were mixed for two minutes along with small amounts of green and amber resin dye to reduce the transparency of the resin. Mix slowly so as to introduce as few bubbles as possible. The bubbles will work their way to the surface and disappear during curing.
Typical of resin applications, a meniscus curve forms at the edges. This is why I have lots of pieces of stone along the banks. After the resin hardened, I carefully added more shale so as to disguise the meniscus curve as much as I could. Small shrubs struggling for survival can be added as well as reeds and grasses in areas where the stream current would not wash them away.
This same technique can be applied when using other types of epoxy resins. Be sure to follow the manufacturer's recommendations for mixing and ventilation.
Another popular product for water is gloss medium. Greater care must be taken when preparing the base of the water area especially when a large body of water is to be modeled. It is imperative that the bottom of the pond is perfectly level. Plywood or similar material would make a good base. It will have to be painted a dark colour to represent deep water. Lighten the colour as you get toward the banks. Underwater objects are a little harder to model as there is relatively no depth to work with. Apply the gloss medium with a brush making sure that you do not overwork the brush strokes. A hair dryer can be used to "blow" ripples onto the surface as it sets up.
Don't forget, surplus supplies can be put to good use as puddles around the engine shops and water tanks.