High-pressure systems are particularly vulnerable to small particles in the water: at very high pressure and flow speeds, even grains of sand can damage turbines and pipelines. Sand traps or filters are therefore required that can remove as much sand and sediment from the water as possible. For this purpose the incoming water is fed into a long basin where the flow is slowed down and calmed. This allows solids to sink to the bottom so that only cleansed water is fed into the turbine. The sediment is periodically flushed out of the basin. The headwater channel connects the outlet/sand trap with the equalising reservoir, and depending on the topography and cost factors it may take the form of an open or closed channel (or in some cases a pipe). The equalising reservoir performs a similar function to that of the sand trap: the flow of the incoming water is slowed down, and sediment can then sink to the bottom. It is also used as a reservoir in order to ensure that a constant volume of water is fed into the turbine despite fluctuations in the water level. Before water flows into the pressure pipe, it has to pass through a very fine grill in order to keep any floating debris away from the turbine. Depending on the location and type of the plant, a headwater channel, equalisation reservoir or sand trap may not be required.
The water is fed into the turbine via a pressure pipe. Since the pressure inside these pipes is often very high, they are usually made of steel, but other materials such as plastics, cast iron, reinforced concrete or wood may be used, depending on the type of power plant.
Practically all turbines are susceptible to damage by floating debris (leaves, pieces of wood, ice, etc.), and a grill is therefore used to protect these valuable machines. Grills may take the form of parallel rods made from a variety of metals, or other structures such as perforated plates. Debris that builds up in front of the grill is removed on a periodical basis - in most modern facilities, this takes place automatically.