A purchase order (PO) is a document you — the plumbing contractor — send to a supplier to authorize a materials purchase before anything ships. It lists exactly what you are ordering (SKUs, quantities, and the prices you agreed on), where it goes, and when you need it. Once the vendor accepts it, the PO becomes a binding order both sides can reference.

You issue a purchase order up front to order materials; the supplier issues an invoice afterward to request payment. The PO says “here is what we want and the price we agreed on,” while the invoice says “here is what we shipped, now pay us.” Matching the two — plus the packing slip — is how you catch overbilling before you cut a check.

A plumbing PO needs your company (buyer) and the vendor’s details, a ship-to address (jobsite or warehouse), a PO number, the order and required-by dates, and line items with SKU/part #, description, quantity, unit, and unit price — water heaters, PEX and fittings, valves, and fixtures. Add payment terms (Net 30 is standard), shipping method, subtotal, sales tax, freight, and a grand total. For bulky items like a 50-gallon heater, note lift-gate delivery and a site contact in the instructions.

The PO number is the unique ID you assign to each order. It is the thread that ties the PO to the vendor’s packing slip and invoice, so your bookkeeper can run a three-way match and confirm you are paying for what you actually received. Require it on every invoice and packing slip and you will spot duplicate or inflated bills fast.

Ship to the jobsite when materials are needed on site and someone will be there to receive them — it saves a trip and gets the crew working sooner. Ship to your warehouse when you want to inspect, stage, or consolidate loads first, or when the site is not secure. Toggle “Ship to my company address” for warehouse delivery, or enter the jobsite address and a site contact for a direct-to-site drop.