You may have thought that deciding to build a pond and where to place it was the hard part but now you have to deciding how to line your pond. In order to make this decision a little easier I have listed the options below with some of the advantages and disadvantages.
Most gardeners no matter how amateur will have heard of the flexible Butyl rubber, Epalyn rubber or PVC liner and the majority will opt for this option which if laid correcting can last anything between 11 and 25 years before it needs replacing. Price is dependant on the size required and material chosen but there is usually something for most budgets. Dont forget you will need to line the hole before laying the liner to stop sharp stones from splitting it. For this you will need soft sand, pieces of old carpet or a pond liner underlay.
Next is the preformed pond liner, made from glass fibre or polyethylene, this type of liner gives and instant shape with built in marginal planting shelves. They come in a range of sizes and shapes, from formal to natural, with a choice of colours. Lasting ten years or more they are disadvantaged against the flexible liner. These start at around £25 for a 74cmx89cmx30cm and the larger the pond the bigger the price tag. These ponds also need protecting so soft sand must be molded to its shape to stop any sharp stones or distorting.
You could choose to create a concrete lined pond although this building method is not as popular as it once was. If the pond you require has a formal look and needs retaining walls you may choose this method. The shape is built with breeze blocks and then skimmed with a mix of sharp sand, cement and fibre glass.
Concrete used to be pored into a shuttered mold to produce a solid concrete structure but after time these structures would shift causing cracks to appear that are difficult to repair.
Another option you may choose is to build your structure from brick, block or another building material and have it covered in glass fibre to water proof it. This method is good for difficult shapes and comes in a wide range of colours but can be a solution for a larger budget as in my experience in can cost upwards of £50 per square meter(inc VAT).
And finally a more natural option is clay lining a tradditional method of puddling is used by shoveling clay covering in enough water to make it flexible and then treading all over it (JCB if large area) to release all the air. This method can be difficult and will require more research. It was used to line canals and other waterways but back then they would drive flocks of sheep or cattle down the waterways to trample all the air out.