{"id":61,"date":"2026-10-03T11:30:31","date_gmt":"2026-10-03T03:30:31","guid":{"rendered":"https:\/\/www.gaodonghe.cn\/?page_id=61"},"modified":"2026-10-15T20:28:26","modified_gmt":"2026-10-15T12:28:26","slug":"guides","status":"publish","type":"page","link":"https:\/\/www.gaodonghe.cn\/?page_id=61","title":{"rendered":"Buyer&#039;s Guide"},"content":{"rendered":"\n<style id=\"crc-read-css\">\n\/* \u9605\u8bfb\u6392\u7248\uff1a\u684c\u9762 *\/\n.entry-content.wp-block-post-content{\n  --wp--style--global--content-size: 680px;\n  font-size: 17.5px;\n  line-height: 1.75;\n}\n.entry-content.wp-block-post-content h1{\n  font-size: clamp(27px, 4vw, 34px);\n  font-weight: 700;\n  line-height: 1.25;\n  letter-spacing: -.01em;\n  margin: 0 0 .7em;\n}\n.entry-content.wp-block-post-content h2{\n  font-size: clamp(22px, 2.7vw, 27px);\n  font-weight: 650;\n  line-height: 1.32;\n  letter-spacing: -.005em;\n  margin: 2.2em 0 .7em;\n}\n.entry-content.wp-block-post-content h3{\n  font-size: clamp(18.5px, 2.2vw, 21px);\n  font-weight: 600;\n  line-height: 1.4;\n  margin: 1.6em 0 .5em;\n}\n.entry-content.wp-block-post-content strong{ font-weight: 650; }\n.entry-content.wp-block-post-content p{ margin: 0 0 1em; }\n.entry-content.wp-block-post-content ul,\n.entry-content.wp-block-post-content ol{ margin: 0 0 1em; padding-left: 1.35em; }\n.entry-content.wp-block-post-content li{ margin: 0 0 .45em; }\n.entry-content.wp-block-post-content img{ max-width: 100%; height: auto; border-radius: 6px; }\n\/* \u8868\u683c\uff1a\u8fb9\u6846 + \u8868\u5934\u5e95\u8272 + \u884c\u8868\u5934\u52a0\u7c97\uff08\u684c\u9762\u9650\u5bbd 600px\uff0c\u4e0d\u518d\u6491\u6ee1\uff09 *\/\n.entry-content.wp-block-post-content table{\n  width: 100%;\n  max-width: 600px;\n  border-collapse: collapse;\n  margin: 0 0 1.2em;\n}\n.entry-content.wp-block-post-content th,\n.entry-content.wp-block-post-content td{\n  border: 1px solid #c9c9c9;\n  padding: .55em .75em;\n  font-size: .92em;\n  text-align: left;\n  vertical-align: top;\n}\n.entry-content.wp-block-post-content thead th{\n  background: #f2f2f2;\n  font-weight: 600;\n}\n.entry-content.wp-block-post-content tbody th[scope=\"row\"]{\n  background: #fafafa;\n  font-weight: 600;\n  white-space: nowrap;\n}\n.entry-content .crc-table-scroll{max-width:600px;margin-left:auto;margin-right:auto}\n\/* \u9605\u8bfb\u6392\u7248\uff1a\u624b\u673a *\/\n@media (max-width: 600px){\n  .entry-content.wp-block-post-content{ font-size: 16.5px; line-height: 1.72; }\n  .entry-content.wp-block-post-content h1{ font-size: 25px; }\n  .entry-content.wp-block-post-content h2{ font-size: 21px; margin-top: 1.9em; }\n  .entry-content.wp-block-post-content h3{ font-size: 18.5px; }\n  \n  .entry-content.wp-block-post-content th,\n  .entry-content.wp-block-post-content td{ padding: .5em .6em; }\n}\n\/* \u4f5c\u8005\u4e0e\u66f4\u65b0\u65f6\u95f4 *\/\n.entry-content .crc-byline{\n  font-size: .88em;\n  color: #6b7280;\n  text-align: center;\n  margin: -.2em 0 1.9em;\n}\n<\/style>\n\n\n\n<p class=\"crc-byline wp-block-paragraph\">Author <a href=\"https:\/\/www.gaodonghe.cn\/?page_id=2\">Donghe Gao<\/a> &middot; Last updated October 14, 2026<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>The order matters more than the brand. First, what is in your water. Second, the rated volume and the flow rate. Third, and last, the brand. Source water decides which technology is right, the two numbers decide what the system costs you over the years, and the brand decides the price, not the quality of the water. This page does not push a product. It sets out the order.<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This is a guide for people choosing a water purifier, not a product page.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\" style=\"margin-top:var(--wp--preset--spacing--30);margin-bottom:var(--wp--preset--spacing--30)\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/www.gaodonghe.cn\/wp-content\/uploads\/2026\/10\/membrane-housing-manufacturing-1024x768.jpg\" alt=\"Ultrafiltration membrane, 316L stainless steel housings and finished units being manufactured and assembled in our own workshop\" width=\"1024\" height=\"768\" class=\"wp-image-83\" srcset=\"https:\/\/www.gaodonghe.cn\/wp-content\/uploads\/2026\/10\/membrane-housing-manufacturing-1024x768.jpg 1024w, https:\/\/www.gaodonghe.cn\/wp-content\/uploads\/2026\/10\/membrane-housing-manufacturing-300x225.jpg 300w, https:\/\/www.gaodonghe.cn\/wp-content\/uploads\/2026\/10\/membrane-housing-manufacturing-768x576.jpg 768w, https:\/\/www.gaodonghe.cn\/wp-content\/uploads\/2026\/10\/membrane-housing-manufacturing.jpg 1400w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">Membrane housings and finished ultrafiltration units &#8212; researched, produced, machined and assembled in our own workshop.<\/figcaption><\/figure>\n\n\n\n\n\n<h2 class=\"wp-block-heading\">1. Start from what is in your water, then pick the technology<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Choosing a home water filter does not start with the unit. It starts with your water. Reverse osmosis was developed to desalinate seawater, and it suits water with heavy metals above the limit or serious scaling. If the source is safe and you want the trace minerals left in, ultrafiltration or nanofiltration is the fit. The core differences between the three technologies:<\/p>\n\n\n<div class=\"crc-table-scroll\" style=\"overflow-x:auto;-webkit-overflow-scrolling:touch\">\n<table><thead><tr><th scope=\"col\">Technology<\/th><th scope=\"col\">Nominal pore size<\/th><th scope=\"col\">Minerals and heavy metals<\/th><th scope=\"col\">Reject water and power<\/th><\/tr><\/thead><tbody><tr><td>Reverse osmosis<\/td><td>About 0.0001 micron<\/td><td>Removed together, calcium and magnesium included<\/td><td>Typically produces reject water; needs power<\/td><\/tr><tr><td>Nanofiltration<\/td><td>About 0.001 micron<\/td><td>Most calcium and magnesium held back, some sodium and potassium pass<\/td><td>Typically produces reject water; needs power<\/td><\/tr><tr><td>Ultrafiltration<\/td><td>0.01\u20130.1 micron<\/td><td>Calcium and magnesium stay in the water, dissolved heavy metals are not removed<\/td><td>No continuous reject water; no power required<\/td><\/tr><\/tbody><\/table>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">Four common source situations. This table is the route map:<\/p>\n\n\n<div class=\"crc-table-scroll\" style=\"overflow-x:auto;-webkit-overflow-scrolling:touch\">\n<table><thead><tr><th scope=\"col\">Your situation<\/th><th scope=\"col\">Pre-filter at the inlet<\/th><th scope=\"col\">Choice under the sink<\/th><th scope=\"col\">Why<\/th><\/tr><\/thead><tbody><tr><td>Municipal water that meets the standard<\/td><td>Usually not needed<\/td><td>Ultrafiltration<\/td><td>Sediment, rust and microbes are what a compliant source still picks up, and 0.01 micron is the fit for them; add an activated carbon stage for taste<\/td><\/tr><tr><td>Older buildings on municipal water<\/td><td>PVDF membrane pre-filter<\/td><td>Ultrafiltration or reverse osmosis<\/td><td>Heavy sediment and rust, so one stage in front extends cartridge life<\/td><\/tr><tr><td>Wells or rivers in polluted areas, or water with serious scaling<\/td><td>PVDF membrane pre-filter<\/td><td>Reverse osmosis<\/td><td>Change to a safe source first; RO only if you cannot, and verify with a test afterwards<\/td><\/tr><tr><td>Wells or rivers you know to be safe from a recent test<\/td><td>PVDF membrane pre-filter<\/td><td>Ultrafiltration or reverse osmosis<\/td><td>These turn cloudy every rainy season, so the pre-filter is not optional; it does not replace the water test<\/td><\/tr><\/tbody><\/table>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">Municipal water that meets the standard is the case people ask about most. Start with your supplier&#8217;s published water quality report \u2014 in the United States, the annual Consumer Confidence Report \u2014 or a test of your own water, and read the result before choosing a water filter. Three points:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">First, compliant municipal tap water keeps its heavy metals and chemical contaminants within the limits set by China&#8217;s national drinking-water standard. What it can pick up on the way to your tap is mainly sediment, rust and microbes from the pipes, and a 0.01 micron membrane holds those back. Add an activated carbon stage to remove chlorine and improve taste.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Second, on a source that already meets the standard, the extra precision of reverse osmosis adds nothing most homes need on that water, and it takes the minerals out along with everything else. WHO, <em>Nutrients in Drinking Water<\/em> (2005): water that has been completely or almost completely demineralized is not suitable for long-term drinking unless it is remineralized. The WHO desalination document gives reference values, calcium 20\u201330 mg\/L and magnesium 10 mg\/L. If you do choose RO, choose a unit with a remineralization stage; ultrafiltration keeps the minerals, so the question does not arise.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Third, scale is not toxic. It is calcium and magnesium coming out of solution, a sign that the water carries minerals. China&#8217;s national drinking-water standard limits total hardness (as CaCO\u2083) at 450 mg\/L, and that is an aesthetic and operational limit rather than a health limit; above about 200 mg\/L you start to see scale when you boil. Only when it affects taste and the life of your appliances is it worth dealing with, through a softener or RO.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Why the pre-filter for older buildings is a PVDF membrane: steel mesh, at roughly 40\u2013100 micron, catches only the larger particles, and it holds back neither bacteria nor colloids. PP sediment cartridges, at 1\u20135 micron, catch most particles but cannot be washed, so a clogged cartridge goes in the bin whole. A <a href=\"\/?page_id=93\">PVDF ultrafiltration membrane<\/a> at 0.1 micron takes manual surface cleaning plus backwash with filtered water, and it recovers most of its flow after fouling, so you clean it and put it back into service. A pre-filter, at a basic level, does two things: it cleans the water up, and it protects the cartridges of the <a href=\"\/?page_id=94\">under-sink purifier<\/a>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">2. Compare rated volume and flow rate before you compare price<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The second thing to look at is two numbers: the flow rate decides what the tap feels like to use, and the rated volume decides how long a cartridge actually lasts.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\" style=\"margin-top:var(--wp--preset--spacing--30);margin-bottom:var(--wp--preset--spacing--30)\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/www.gaodonghe.cn\/wp-content\/uploads\/2026\/10\/four-stage-composite-cartridge-819x1024.jpg\" alt=\"Filtration diagram of the four-stage composite cartridge: pleated PP sediment filter, activated carbon fiber, melt-blown PP sediment filter and the PVC ultrafiltration membrane\" width=\"819\" height=\"1024\" class=\"wp-image-85\" srcset=\"https:\/\/www.gaodonghe.cn\/wp-content\/uploads\/2026\/10\/four-stage-composite-cartridge-819x1024.jpg 819w, https:\/\/www.gaodonghe.cn\/wp-content\/uploads\/2026\/10\/four-stage-composite-cartridge-240x300.jpg 240w, https:\/\/www.gaodonghe.cn\/wp-content\/uploads\/2026\/10\/four-stage-composite-cartridge-768x960.jpg 768w, https:\/\/www.gaodonghe.cn\/wp-content\/uploads\/2026\/10\/four-stage-composite-cartridge.jpg 1122w\" sizes=\"auto, (max-width: 819px) 100vw, 819px\" \/><figcaption class=\"wp-element-caption\">The four-stage composite cartridge: sediment pre-filter, activated carbon fiber, melt-blown PP, and a 0.01-micron PVC membrane.<\/figcaption><\/figure>\n\n\n\n\n<div class=\"crc-table-scroll\" style=\"overflow-x:auto;-webkit-overflow-scrolling:touch\">\n<table><thead><tr><th scope=\"col\">Unit<\/th><th scope=\"col\">Output per minute<\/th><th scope=\"col\">Filling a 125 ml (4.2 US fl oz) cup<\/th><\/tr><\/thead><tbody><tr><td>Reverse osmosis (400G)<\/td><td>About 1.05 L\/min (0.28 US gpm)<\/td><td>About 7 seconds<\/td><\/tr><tr><td>Reverse osmosis (800G)<\/td><td>About 2.1 L\/min (0.55 US gpm)<\/td><td>About 4 seconds<\/td><\/tr><tr><td>Reverse osmosis (1200G)<\/td><td>About 3.15 L\/min (0.83 US gpm)<\/td><td>About 2.5 seconds<\/td><\/tr><tr><td>Under-sink ultrafiltration purifier (0.01 micron)<\/td><td>About 8\u201310 L\/min (2.1\u20132.6 US gpm)<\/td><td>About 1 second<\/td><\/tr><\/tbody><\/table>\n<\/div>\n\n<div class=\"crc-table-scroll\" style=\"overflow-x:auto;-webkit-overflow-scrolling:touch\">\n<table><thead><tr><th scope=\"col\">Tier<\/th><th scope=\"col\">Rated total volume<\/th><\/tr><\/thead><tbody><tr><td>Entry<\/td><td>4,000\u20136,000 L (about 1,060\u20131,590 US gal)<\/td><\/tr><tr><td>Mid-range<\/td><td>8,000\u201312,000 L (about 2,110\u20133,170 US gal)<\/td><\/tr><tr><td>Premium RO with a long-life membrane<\/td><td>Claimed up to 50,000 L (about 13,200 US gal)<\/td><\/tr><tr><td>Our under-sink ultrafiltration purifier<\/td><td>100,000 L (about 26,400 US gal), measured in our own factory laboratory rather than by a third-party certified report<\/td><\/tr><\/tbody><\/table>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">RO flow is converted at 1 US gallon \u2248 3.785 liters; the under-sink ultrafiltration figures are measured at household water pressure, and the RO figures are rated daily output averaged over the day rather than instant faucet flow, so a tank-type RO can pour faster for the first few liters. The tier figures are common ranges in the market, and the RO figure is the maker&#8217;s claim, so go by what each brand states. Flow rate and rated volume both hold on one condition: compliant municipal tap water at household water pressure. Flushing and backwash on an ultrafiltration unit use a small amount of water, and power needs depend on the configuration.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Both numbers are on China&#8217;s water-contact approval document for the unit. Before you buy, ask for the rated volume of each cartridge, not just the replacement interval. Cartridges are consumables, and when the volume is used up the cartridge is spent: one maker prints 18 months while the rated volume is only 4,000 L, and the volume runs out first. China&#8217;s national water-efficiency standard makes rated total volume a mandatory figure, with Tier 1 water efficiency requiring no less than 4,000 L; that standard applies to reverse osmosis and nanofiltration units rather than ultrafiltration, but the principle holds the same.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">One more trap: do not go by a single whole-unit volume on the box. Some sellers take the cartridge with the largest volume and label that as the whole-unit figure, which looks good but is not the pace at which the cartridges need replacing. Compare the rated volume membrane by membrane, look at every cartridge, and take the shortest one. The cartridge that reaches its limit first is the one that sets the real replacement rhythm of the unit. Check the time limit as well as the volume, because whichever comes first sets the schedule.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">3. The brand comes last<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The last step is the brand. Large brands are usually stronger on service, certification and consistency, and that much is true. They also cost more, and not all of that difference goes into materials and process; many purifiers sold under a large brand come out of a contract factory in the first place.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Our suggestion: when the budget is limited, look at factory brands first. Be clear about the interest here, though, because we are a factory brand ourselves, and that sentence is a disclosure of interest. You do not have to buy ours. It is worth asking how much of the price goes into materials and process. The test is plain: is there a water-contact approval issued in China, are there third-party test reports, and will the maker put the rated volume on the label. In the end, that is all you can check.<\/p>\n\n\n\n\n\n<h2 class=\"wp-block-heading\">Common questions<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Is a more expensive water purifier better?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">No. A more expensive unit filters finer and flows faster, but on compliant municipal water that precision adds nothing most homes need, and it takes the minerals out with it. The point of choosing is to match the source, not to stack up specifications.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">For long-term drinking, is reverse osmosis or ultrafiltration better?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">On a source that meets the standard, ultrafiltration keeps calcium and magnesium in the water, which sits better with the WHO position that demineralized water is not for long-term drinking; RO is also a choice, ideally with a remineralization stage. Where the source carries heavy metals or excess hardness, RO is the right answer.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Does a purifier need a pre-filter in front of it?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">It depends on the source. In a new building with clear water you can leave it out. In older buildings, where the water runs yellow after a shutdown, or with well and spring water, fit a cleanable PVDF membrane pre-filter first, not to make the water drinkable but to keep the cartridges inside from clogging so fast.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">To close: read your water first, then the two numbers, and price last. Get the order wrong and a bigger budget still buys the wrong unit.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Sources<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">1. WHO, <em>Nutrients in Drinking Water<\/em> (2005): water that is completely or almost completely demineralized is not suitable for long-term drinking unless it is remineralized; the desalination document suggests calcium 20\u201330 mg\/L and magnesium 10 mg\/L, and the discussion sits in its chapter on the health risks of demineralized water.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">2. China&#8217;s national drinking-water standard: total hardness (as CaCO\u2083) limited to 450 mg\/L as an aesthetic and operational limit; above 200 mg\/L, scale appears on boiling.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">3. China&#8217;s national water-efficiency standard: Tier 1 means a recovery rate of at least 65% and a rated total volume of at least 4,000 L, and it applies to reverse osmosis and nanofiltration units rather than ultrafiltration.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">4. Rated volume is measured under defined test conditions, so it is the main replacement criterion rather than an absolute failure point, and the interval printed on the housing is only a rough guide.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">5. Pre-filter pore sizes are standard industry figures; a coarse steel mesh holds back only the larger particles; RO flow is converted at 1 US gallon \u2248 3.785 liters.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">6. Published product figures (PVC 0.01 micron composite cartridge, PVDF 0.1 micron membrane pre-filter); 100,000 L is measured in our own factory laboratory rather than by a third-party certified report, and specifications are set in the technical agreement.<\/p>\n\n\n<p class=\"wp-block-paragraph\"><strong>Related:<\/strong> <a href=\"\/?page_id=64\">Donghe Gao home page<\/a> &middot; <a href=\"\/?page_id=93\">whole-house PVDF pre-filter<\/a> &middot; <a href=\"\/?page_id=94\">PVC under-sink water filter<\/a><\/p>\n\n\n<script type=\"application\/ld+json\">\n{\"@context\": \"https:\/\/schema.org\", \"@type\": \"FAQPage\", \"mainEntity\": [{\"@type\": \"Question\", \"name\": \"Is a more expensive water purifier better?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"No. A more expensive unit filters finer and flows faster, but on compliant municipal water that precision adds nothing most homes need, and it takes the minerals out with it. 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Start with your water quality, compare published performance, then check flow rate, filter life, and maintenance costs.<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-61","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.gaodonghe.cn\/index.php?rest_route=\/wp\/v2\/pages\/61","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.gaodonghe.cn\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.gaodonghe.cn\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.gaodonghe.cn\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.gaodonghe.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=61"}],"version-history":[{"count":16,"href":"https:\/\/www.gaodonghe.cn\/index.php?rest_route=\/wp\/v2\/pages\/61\/revisions"}],"predecessor-version":[{"id":237,"href":"https:\/\/www.gaodonghe.cn\/index.php?rest_route=\/wp\/v2\/pages\/61\/revisions\/237"}],"wp:attachment":[{"href":"https:\/\/www.gaodonghe.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=61"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}