You can purchase plumbing supply materials from several places (these are in no particular order).
Big box hardware stores like Home Depot, Lowes, or Menards are the most well known. You can also visit your local hardware store like Ace or True Value, for example. Industrial supply houses mostly sell to businesses and contractors and will sell everything industrial; from material moving equipment to safety equipment and plumbing material. Some examples are Grainger and McMaster Carr. You can also browse the internet for e-commerce or on-line plumbing supply houses. These suppliers can offer everything from a few niche items to anything you can possibly imagine. Professional plumbing supply houses are another possibility. Many of them will only sell to professionals who carry credit lines, but some (the number is increasing everyday) are finding it exceedingly difficult to turn away cash paying customers (professional or not).
How do I Decide Where to Buy My Plumbing Stuff?
If you are a consumer and looking for material to do a simple repair the big box store should have what you need. They carry basic plumbing rough-in material and name brand fixtures. Their pricing on common items is very good, however, if you have a repair that requires uncommon materials (materials that they do not carry in-stock), the big box may not be the best place to purchase. Remember, the reason pricing on “common” materials is great at a big box is because of the tremendous volume they buy from manufacturers. If an item in not in-stock, they are not buying it in tremendous volume. Therefore, they do not carry the discount the in-stock item would.
Your local hardware store will carry a limited amount of plumbing materials (nowhere near the volume of the big box stores), but you will probably pay more for the same items you will find in the big box store (see above). Mostly, local hardware stores should be used when you are in a pinch. You may be able to find some private label fixtures that are pretty durable and competitively priced.
For materials or fixtures in large quantities, an industrial supply house or plumbing supply house/wholesaler can give you some very competitive pricing. However, for everyday plumbing supplies, these options are not very practical.
For both professionals and consumers, the best pricing will invariably come from e-commerce sites or on-line plumbing stores. Because these companies have less overhead (physical space, salespeople, distribution, etc) they can, and do, offer materials at a lower price. The downside is that you are buying from a “faceless” entity. You cannot go to the store any physically browse the aisles or talk to a salesperson or clerk. If you know what you are looking for, this can be a very cost effective way to purchase your plumbing supplies.