At the decoration or engineering site, people often ask: "PVC water supply pipes and drain pipes look similar, can they be mixed? Save the trouble of purchasing separately." In fact, the answer is very clear - no! There are essential differences between the two from material formula to performance design, and mixing may bury hidden dangers of safety or waste. Let's talk about the difference in material formula first. PVC water supply pipes are "sanitary customized models": the raw materials are PVC resins that meet drinking water standards, and the additives (such as stabilizers and lubricants) are all food grade to ensure that long-term contact with tap water will not precipitate lead, cadmium and other harmful substances. And PVC drain pipes are "practical grade formula": in order to reduce costs, fillers such as calcium carbonate may be added, and even partially recycled PVC may be used. Most of the stabilizers are industrial grade (as long as the drainage needs are met). Simply put, the water supply pipe is "a safe material that can come into contact with drinking water", and the drain pipe is "an economical material suitable for sewage water", and the formula direction is completely different. Then look at the specificity of the performance design. The core requirement of the water supply pipe is "pressure resistance + hygiene": tap water is under pressure (generally 0.3-0 MPa in households, and the upper level may reach 1.0 MPa), so the pressure level of the water supply pipe is at least 1.0 MPa or more, and the pipe wall is thicker and more uniform, which can withstand long-term pressure; at the same time, the inner wall must be smooth to reduce the resistance of water flow, and it must pass the GB/T 17219 drinking water hygiene standard test. The core requirement of the drain pipe is "unobstructed + impact-resistant": the drain is a gravity flow (no pressure, flowing downwards by gravity), so the pressure level is only below 0.6MPa, and the pipe wall is thinner; but to deal with the impact of debris in the sewage (such as the residue of vegetable washing water, the water flushed by the toilet), so more emphasis is placed on impact resistance, rather than pressure. The most crucial thing is the gap in hygienic performance. The water supply pipe is used to transport drinking water, and it must be "zero harm" - the inner wall cannot have peculiar smell, the additives cannot be toxic, and even long-term soaking will not pollute the water. The drain pipe does not have this requirement: it is exposed to sewage and wastewater, as long as it can be discharged, it does not consider whether it can be drunk or not. If the drain pipe is used as a water supply pipe, industrial-grade additives will be integrated into drinking water. For example, excessive lead may cause intellectual development problems in children and gastrointestinal discomfort in adults. On the other hand, when the water supply pipe is used as a drain pipe, although there will be no hygiene problems, the design of thick pipe walls and high pressure levels is completely "overkill", which is a waste of money. There are also hidden dangers of pressure-bearing capacity. For example, connecting the drain pipe to the water supply pipe: when the tap water pressure comes, the drain pipe cannot withstand it at all - it was originally designed for gravity flow, the pipe wall is thin, the pressure level is low, and it is likely to burst and leak, soaking the home; while the water supply pipe is used for drainage, although it will not burst, you spend the money on the water supply pipe, but it is used in places that do not need to bear pressure, which is equivalent to "using BMW to pull goods" and wasting costs. To sum up: PVC water supply pipes and drain pipes seem similar, but in fact they are two kinds of pipes that "perform their duties" - the water supply pipe is responsible for "safely delivering water to the home", and the drain pipe is responsible for "smoothly draining sewage". Mixed use either sacrifices hygiene and safety (the drain pipe is used as water supply), or wastes money (the water supply pipe is used as drainage), and even causes accidents such as pipe bursts and water leaks. So whether it is decoration or engineering, you must choose the right pipe according to the purpose, and don't bury hidden dangers because of "saving trouble".