Common parts to a small man made pond may include:

Liner: When building a lined pond use a 45 mil to 60 mil thick fish-safe EPDM for longevity and puncture resistance. An under layer should be placed under the liner after sand and compacted earth have been properly established. If large boulders are being placed in the pond a geo-trextile membrane should be placed on top of the liner to prevent granite corners or jagged rock edges from compromising the liner. Leaking ponds are no fun to fix.

Skimmer: The typical skimmer allows water to be drawn from the surface of the pond and can be outside of the pond connected to the liner as a pump vault or can be inside the pond as a satellite pond skimmer or free-floating skimmer. It collects leaves, pollen, twigs, uneaten food and all other kinds of floating debris. The skimmer usually has a collection basket that can be quickly emptied on a regular basis to allow the skimmer to run properly. Floating skimmers may also have a foam filter insert that sits underneath the basket to filter out the finer particles. Brushes to prevent fish from entering the skimmer mouth are also available in some models or can be added manually.

Bottom drains: Bottom drains are usually not required in small water gardens or shallow goldfish ponds but can be very beneficial for larger Koi ponds. A  bottom drain allows any heavy solid particulate to be drawn out the drain and carried to the mechanical filtration system. Some bottom drains are equipped with EPDM membrane fine bubble diffusers which are connected to air pumps on shore which help create circulation and improve the draining effect and of course adding much needed oxygen to a pond at the lowest point which is very efficient.

Mechanical filter: Mechanical filtration can be achieved using many different techniques but the principle goal remains constant: the job of tha mechanical filter is to trap solids, preventing them from clogging the biological filter or reducing the effectiveness of the growing biofilm on the matrix inside the biofilter. The mechanical filter should be backwashed or cleaned out often. Types of mechanical filters include Vortex, brushes, matting, sand and gravel, sieve screen, and settlement chamber. Mesh bags and common Matala foam materials can be used to create homemade pond filters using basic plumbing parts and a thorough understanding of how the pump intake can be used to draw material through the filter.

Biological filter: Biological filters convert the nitrogenous wastes from the fish and offer a vibrant habitat for bacteria.  A biofilter can be constructed in many different ways and in each case the purpose of the filter is to provide the maximum surface area for beneficial cleaning biofilm to develop and thrive so that the water is being cleaned naturally and without the overuse of chemicals. It is important for the koi keeper to understand how the filter is to be cleaned before they install one. Proper and regular cleaning of the mechanical and biological filters is a key factor in contribution for the health and quality of the koi and the entire pond. Bio-filters are sometimes divided into sub groups such as aerated or non-aerated and there are a variety of types of bio-filters to match the required parameters of filtration and pond capacity including aerated types like the moving bed filters and Bakki shower or Trickle filters and the non-aerated variety which include sand filters, cross-flow-filters and the pressurized and bead filters. 

Ultraviolet light: Ultraviolet clarifiers are used to make algae flocculate so that the clumped algae can be removed via the mechanical filtration. A UV sterilizer will also kill free-floating bacteria in the pond water.

Water and air pumps: Pond pumps are used to create waterfalls and fountain sprays and should be sized to the considerations of tubing diameters, hose lengths, hydro-static head etc. A waterfall pump should give about 100 gallons of flow per hour per inch of width as a general rule. While the aesthetic use of pumps is important the most important pumping job of the Water pump is to move water through the filter system and back to the pond in a recirculating manner at the correct volume. The important thing to understand about pumps is that they be sized to the pond and the filter system. The pump should be circulating the total volume of water at least once per hour for proper water quality. UV filters and clarifiers and mechanical filters all have maximum flow recommendations which should be adhered to.

An air pump can be used to increase dissolved oxygen. In a heavily stocked fish pond, an air pump is a necessity. Air pumps and diffusers can also be used to over winter fish. Designing an aeration system means choosing the correct CFM air flow from the pump along with the output pressure range of the pump and the style of diffuser being used; ie; coarse bubble diffusers or micro-bubble diffusers or bubble tubing in stocking pens.