{"id":122,"date":"2026-05-18T15:35:20","date_gmt":"2026-05-18T10:35:20","guid":{"rendered":"https:\/\/watertankcalculator.com\/guides\/?p=122"},"modified":"2026-10-10T11:08:39","modified_gmt":"2026-10-10T06:08:39","slug":"how-gravity-feed-water-systems-work","status":"publish","type":"post","link":"https:\/\/watertankcalculator.com\/guides\/how-gravity-feed-water-systems-work\/","title":{"rendered":"How Gravity-Feed Water Systems Work (and Their Limits)"},"content":{"rendered":"\n<p>A gravity-feed water system uses height in place of a pump. The tank sits above the taps, and the weight of the water in the pipe pushes it out when a tap opens. <strong>Every metre of height between the water surface and the tap gives about 0.1 bar (1.42 psi) of pressure<\/strong>, so a tank 5 m up delivers roughly 0.5 bar. Nothing else adds to that figure: not the size of the tank, not its shape, not the width of the pipe.<\/p>\n\n\n\n<p>That makes gravity feed simple, silent and immune to power cuts, and it also sets a hard ceiling. This guide explains how the pressure and the flow are decided, what you can run at each height, where gravity feed stops working, and how to get the most from the height you have.<\/p>\n\n\n\n<div class=\"wp-block-group has-background has-global-padding is-layout-constrained wp-container-core-group-is-layout-30e86add wp-block-group-is-layout-constrained\" style=\"border-radius:8px;background-color:#eef6fb;padding-top:1.25rem;padding-right:1.5rem;padding-bottom:1.25rem;padding-left:1.5rem\">\n<p><strong>Quick answer<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Pressure comes from height only:<\/strong> 0.1 bar per metre, or 0.433 psi per foot.<\/li>\n\n\n\n<li><strong>Flow comes from the pipe:<\/strong> with so little pressure to spend, pipe bore decides how much water arrives.<\/li>\n\n\n\n<li><strong>A shower works from 1 m of head<\/strong> with a low-pressure head, and is comfortable from about 5 m.<\/li>\n\n\n\n<li><strong>The top floor always gets the least.<\/strong> Check the highest shower first.<\/li>\n\n\n\n<li><strong>Not enough height?<\/strong> Use larger pipe and low-pressure fittings before reaching for a pump.<\/li>\n<\/ul>\n\n\n\n<div class=\"wp-block-buttons is-layout-flex wp-block-buttons-is-layout-flex\">\n<div class=\"wp-block-button\"><a class=\"wp-block-button__link wp-element-button\" href=\"https:\/\/watertankcalculator.com\/calculators\/pressure\/gravity-feed-flow-rate-calculator\">Open the Gravity Feed Flow Rate Calculator<\/a><\/div>\n<\/div>\n<\/div>\n\n\n\n<h2 class=\"wp-block-heading\">How gravity creates pressure<\/h2>\n\n\n\n<p>Water has weight, and a column of it presses down on whatever is at the bottom. The taller the column, the greater the pressure. The formula is P = \u03c1 \u00d7 g \u00d7 h, which for water works out to about 9.8 kPa for every metre of height. Plumbers call that height the <strong>head<\/strong>.<\/p>\n\n\n\n<p class=\"has-background\" style=\"background-color:#eaf7ee\"><strong>Example:<\/strong> the water surface in a rooftop tank is 4 m above a kitchen tap. Pressure at the tap = 4 \u00d7 0.098 = <strong>0.39 bar (5.7 psi)<\/strong>.<\/p>\n\n\n\n<p>Head is measured straight down, from the water surface in the tank to the outlet you are using. The length and route of the pipe do not change it. Two details matter when you measure:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Use the low-water level.<\/strong> As the tank empties, the surface drops and the pressure drops with it. Measure from the tank&#8217;s outlet, which is the worst case, not from the brim.<\/li>\n\n\n\n<li><strong>Measure to the outlet itself.<\/strong> A shower head is about 2 m above the floor, so it has 2 m less head than a tap at floor level in the same room.<\/li>\n<\/ul>\n\n\n\n<p>For the units and the conversions, see <a href=\"https:\/\/watertankcalculator.com\/guides\/water-pressure-explained-psi-bar-and-kpa\/\">water pressure explained in psi, bar and kPa<\/a>. The <a href=\"https:\/\/watertankcalculator.com\/calculators\/pressure\/water-pressure-calculator\">Water Pressure Calculator<\/a> turns your tank and outlet heights into pressure. The same physics sets the load on the tank walls, which is covered in <a href=\"https:\/\/watertankcalculator.com\/guides\/what-is-hydrostatic-pressure-and-how-does-it-affect-tank-design\/\">what hydrostatic pressure is and how it affects tank design<\/a>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">What you can run at each height<\/h2>\n\n\n\n<figure class=\"wp-block-table is-style-stripes\"><table class=\"has-fixed-layout\"><thead><tr><th>Head<\/th><th>bar<\/th><th>psi<\/th><th>What it supports<\/th><\/tr><\/thead><tbody><tr><td><strong>1 m<\/strong><\/td><td>0.10<\/td><td>1.4<\/td><td>Taps at a slow flow. The minimum for a gravity mixer shower with a low-pressure head<\/td><\/tr><tr><td><strong>2 m<\/strong><\/td><td>0.20<\/td><td>2.8<\/td><td>Usable taps. The minimum inlet pressure of some top-loading washing machines<\/td><\/tr><tr><td><strong>3 m<\/strong><\/td><td>0.29<\/td><td>4.3<\/td><td>A workable shower with a low-pressure head<\/td><\/tr><tr><td><strong>5 m<\/strong><\/td><td>0.49<\/td><td>7.1<\/td><td>A comfortable shower; good flow at taps<\/td><\/tr><tr><td><strong>7 m<\/strong><\/td><td>0.69<\/td><td>10.0<\/td><td>Equal to the guaranteed minimum for UK mains (7 m static head)<\/td><\/tr><tr><td><strong>10 m<\/strong><\/td><td>0.98<\/td><td>14.2<\/td><td>Equal to the 10 m of head UK water companies aim to deliver at the boundary<\/td><\/tr><tr><td><strong>14 m<\/strong><\/td><td>1.4<\/td><td>20<\/td><td>The lowest pressure many mains-type shower heads and washing machines are built for<\/td><\/tr><\/tbody><\/table><figcaption class=\"wp-element-caption\">Pressures are static, before pipe losses. Shower and appliance figures come from the manufacturer documents cited below.<\/figcaption><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\">Showers<\/h3>\n\n\n\n<p>UK shower maker Mira describes the classic gravity system as a cold tank in the loft with its base typically at least 1 metre above the showerhead, and rates its shower fittings from a minimum maintained pressure of 0.1 bar. Its low-pressure spray plate is made for &#8220;pressures between 0.1 and 0.5 bar (1 m to 5 m head)&#8221; (<a href=\"https:\/\/resources.kohler.com\/plumbing\/mira\/pdf\/1095475-w2-mira-energise-and-l10-shower-fittings-guide.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">Mira fittings guide<\/a>). So a gravity shower is possible from 1 m, workable at about 3 m and comfortable at about 5 m, provided the shower head is the low-pressure kind.<\/p>\n\n\n\n<p>The <a href=\"https:\/\/watertankcalculator.com\/calculators\/pressure\/minimum-tank-height-for-shower-pressure-calculator\">Minimum Tank Height for Shower Pressure Calculator<\/a> works out the height you need for a chosen pressure. If you already have a weak shower, see <a href=\"https:\/\/watertankcalculator.com\/guides\/why-is-my-shower-pressure-low-even-with-a-full-rooftop-tank\/\">why shower pressure is low even with a full rooftop tank<\/a>.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Washing machines and other appliances<\/h3>\n\n\n\n<p>There is no single figure, because machines are built for different markets. Check the manual before you buy:<\/p>\n\n\n\n<figure class=\"wp-block-table is-style-stripes\"><table class=\"has-fixed-layout\"><thead><tr><th>Machine<\/th><th>Minimum inlet pressure<\/th><th>Head needed<\/th><\/tr><\/thead><tbody><tr><td><a href=\"https:\/\/media3.bosch-home.com\/Documents\/9001792021_A.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">Bosch ExpertCare top-loader<\/a><\/td><td>20 kPa (0.2 bar)<\/td><td>About 2 m<\/td><\/tr><tr><td><a href=\"https:\/\/media3.bosch-home.com\/Documents\/9001345015_A.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">Bosch C series top-loader<\/a><\/td><td>30 kPa (0.3 bar)<\/td><td>About 3 m<\/td><\/tr><tr><td><a href=\"https:\/\/www.samsung.com\/hk_en\/support\/home-appliances\/what-range-should-the-water-pressure-be-for-samsung-washing-machine\" target=\"_blank\" rel=\"noreferrer noopener\">Samsung washing machines<\/a><\/td><td>20 psi (1.4 bar)<\/td><td>About 14 m<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>The difference is sevenfold. A machine rated from 0.2 bar will fill from a tank on a single-storey roof. One rated from 1.4 bar will not, and Samsung warns that below its minimum the water valve can fail or stop shutting off completely. In a tank-fed home, the pressure rating belongs on the shopping list next to the drum size.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Pressure is not flow: why the pipe matters so much<\/h2>\n\n\n\n<p>The figures above are <strong>static pressure<\/strong>, measured with every tap closed. Once water moves, friction against the pipe wall uses some of it up, and what reaches the outlet is lower. In a mains system with 3 or 4 bar to spare, nobody notices. In a gravity system with 0.3 or 0.5 bar in total, the pipe can take most of it.<\/p>\n\n\n\n<p>The table shows the pressure left at the outlet, in bar, after 20 m of pipe:<\/p>\n\n\n\n<figure class=\"wp-block-table is-style-stripes\"><table class=\"has-fixed-layout\"><thead><tr><th>Head and pipe bore<\/th><th>Static<\/th><th>One shower (9 L\/min)<\/th><th>Shower plus a tap (18 L\/min)<\/th><\/tr><\/thead><tbody><tr><td><strong>3 m head, 15 mm<\/strong><\/td><td>0.29<\/td><td>0.17<\/td><td>Cannot be reached<\/td><\/tr><tr><td><strong>3 m head, 20 mm<\/strong><\/td><td>0.29<\/td><td>0.26<\/td><td>0.18<\/td><\/tr><tr><td><strong>3 m head, 25 mm<\/strong><\/td><td>0.29<\/td><td>0.28<\/td><td>0.26<\/td><\/tr><tr><td><strong>5 m head, 15 mm<\/strong><\/td><td>0.49<\/td><td>0.37<\/td><td>0.04<\/td><\/tr><tr><td><strong>5 m head, 20 mm<\/strong><\/td><td>0.49<\/td><td>0.46<\/td><td>0.38<\/td><\/tr><tr><td><strong>5 m head, 25 mm<\/strong><\/td><td>0.49<\/td><td>0.48<\/td><td>0.45<\/td><\/tr><\/tbody><\/table><figcaption class=\"wp-element-caption\">Hazen-Williams equation, smooth plastic pipe (C = 150), internal diameter, straight pipe only. Bends and valves take a little more.<\/figcaption><\/figure>\n\n\n\n<p>Read the 15 mm rows. With 5 m of head, one shower runs well at 0.37 bar. Open a tap as well and the pressure falls to almost nothing, because pushing 18 L\/min through that pipe takes nearly all 5 metres. With 3 m of head, the pipe cannot carry that flow at all. In 25 mm pipe, the second outlet barely registers.<\/p>\n\n\n\n<p class=\"has-background\" style=\"background-color:#eef6fb\"><strong>This is the most important design rule in gravity feed:<\/strong> height sets the pressure, but pipe bore decides whether you keep it. A bigger tank does nothing for either.<\/p>\n\n\n\n<p>The <a href=\"https:\/\/watertankcalculator.com\/calculators\/pressure\/gravity-feed-flow-rate-calculator\">Gravity Feed Flow Rate Calculator<\/a> uses the same equation to give the flow for your own head, pipe bore and length. For a pipe fed from a pressurised supply, use the <a href=\"https:\/\/watertankcalculator.com\/calculators\/flow\/pipe-size-flow-rate-calculator\">Pipe Size and Flow Rate Calculator<\/a>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">The limits of gravity feed<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">1. Pressure is capped by the building<\/h3>\n\n\n\n<p>One bar needs 10 metres. A house cannot offer much more than its own height, so a gravity system in an ordinary home tops out well below mains pressure. Fittings that expect mains pressure will disappoint on it.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">2. The top floor gets the least<\/h3>\n\n\n\n<p>Head is counted from the tank down, so the bathroom nearest the tank has the weakest shower. Take a tank on a 1 m stand on a flat roof, with a 3 m ceiling below and a shower head 2 m above the floor:<\/p>\n\n\n\n<figure class=\"wp-block-table is-style-stripes\"><table class=\"has-fixed-layout\"><thead><tr><th>Outlet<\/th><th>Head<\/th><th>Pressure<\/th><\/tr><\/thead><tbody><tr><td>Top-floor shower head<\/td><td>About 2 m<\/td><td>0.2 bar<\/td><\/tr><tr><td>Top-floor basin tap (0.9 m above floor)<\/td><td>About 3 m<\/td><td>0.3 bar<\/td><\/tr><tr><td>Shower head one floor down<\/td><td>About 5 m<\/td><td>0.5 bar<\/td><\/tr><tr><td>Shower head two floors down<\/td><td>About 8 m<\/td><td>0.8 bar<\/td><\/tr><\/tbody><\/table><figcaption class=\"wp-element-caption\">Each 3 m storey adds about 0.3 bar. Slab thickness adds a little more.<\/figcaption><\/figure>\n\n\n\n<p>For buildings with several floors, <a href=\"https:\/\/watertankcalculator.com\/guides\/how-to-size-a-rooftop-water-tank-for-a-multi-storey-building\/\">how to size a rooftop water tank for a multi-storey building<\/a> covers the layout in more depth.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">3. Flow is capped by the pipe<\/h3>\n\n\n\n<p>As the table in the last section shows, a narrow pipe can supply one outlet and fail on two. No amount of storage fixes that.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">4. Air can block the pipe<\/h3>\n\n\n\n<p>Low-pressure pipes are easily stopped by trapped air. Air collects at any high point in the pipe run, and each pocket costs head equal to its own height. If the pockets add up to more than the head available, an engineering manual on the subject notes, &#8220;this air acts as a block so that no water at all comes out at the end of the pipe&#8221; (<a href=\"https:\/\/bdd.pseau.org\/outils\/ouvrages\/aplv_air_in_pipes_manual_en.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">Corcos, Air in Water Pipes<\/a>). A pump would force the air through. Gravity often cannot. The cure is in the layout: pipes that fall continuously from the tank, with no humps.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">5. Pressure falls as the tank empties<\/h3>\n\n\n\n<p>The effect is small but real. A tank holding 1 m of water gives 0.1 bar less when nearly empty than when full. On a system with only 0.3 bar to begin with, that is a third of it.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">How to get the most from the height you have<\/h2>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Use 25 mm bore pipe from the tank.<\/strong> Run the main feed in 25 mm and step down only at the final branch to each outlet. This is the cheapest gain available, and rainwater designer Brad Lancaster makes it his standard for gravity-fed cisterns.<\/li>\n\n\n\n<li><strong>Fit full-bore valves.<\/strong> Many stop valves are narrower inside than the pipe. On a low-pressure line such constrictions &#8220;can greatly reduce the flow volume and velocity of water from a gravity-fed cistern&#8221; (<a href=\"https:\/\/www.harvestingrainwater.com\/rainwater-harvesting-inforesources\/suppliers\/full-port-valves-for-gravity-fed-tankscisterns\/\" target=\"_blank\" rel=\"noreferrer noopener\">Lancaster<\/a>). Use full-bore ball or gate valves.<\/li>\n\n\n\n<li><strong>Keep the pipe falling all the way.<\/strong> No rises and dips where air can collect. Where a hump cannot be avoided, fit a vent at the high point.<\/li>\n\n\n\n<li><strong>Keep runs short and straight.<\/strong> Every metre and every elbow costs head you cannot spare.<\/li>\n\n\n\n<li><strong>Buy fittings made for low pressure.<\/strong> Low-pressure shower heads and taps have larger waterways. Check appliance manuals for the minimum inlet pressure.<\/li>\n\n\n\n<li><strong>Give the shower its own pipe from the tank.<\/strong> Then a tap opening elsewhere cannot rob it.<\/li>\n\n\n\n<li><strong>Raise the tank, if the structure allows.<\/strong> Each metre of stand adds 0.1 bar. It also lifts a load of a tonne per 1,000 litres higher above the roof, so check it first.<\/li>\n\n\n\n<li><strong>Boost one outlet, not the whole house.<\/strong> If only the top-floor shower is weak, a small pump on that line keeps everything else on gravity.<\/li>\n<\/ol>\n\n\n\n<p class=\"has-background\" style=\"background-color:#fff4e0\"><strong>Before raising or enlarging a rooftop tank:<\/strong> a full 2,000 L tank weighs over 2 tonnes. Run the <a href=\"https:\/\/watertankcalculator.com\/calculators\/weight\/rooftop-load-bearing-calculator\">Rooftop Load Bearing Calculator<\/a> or the <a href=\"https:\/\/watertankcalculator.com\/calculators\/weight\/safe-rooftop-tank-load-calculator\">Safe Rooftop Tank Load Calculator<\/a>, read <a href=\"https:\/\/watertankcalculator.com\/guides\/will-my-roof-hold-a-full-water-tank\/\">will my roof hold a full water tank<\/a>, and have a structural engineer confirm the position and the stand.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">The parts of a gravity-feed system<\/h2>\n\n\n\n<figure class=\"wp-block-table is-style-stripes\"><table class=\"has-fixed-layout\"><thead><tr><th>Part<\/th><th>What it does<\/th><th>What to get right<\/th><\/tr><\/thead><tbody><tr><td><strong>Elevated tank<\/strong><\/td><td>Stores water and provides the head<\/td><td>A base that supports the whole floor of the tank<\/td><\/tr><tr><td><strong>Inlet with float valve<\/strong><\/td><td>Refills the tank and shuts off when full<\/td><td>A valve suited to your supply pressure<\/td><\/tr><tr><td><strong>Lid and screened vent<\/strong><\/td><td>Lets air in as water leaves; keeps dirt, light and insects out<\/td><td>A rigid, close-fitting, fixed lid<\/td><\/tr><tr><td><strong>Overflow pipe<\/strong><\/td><td>Carries water away safely if the float valve fails<\/td><td>An insect screen with mesh no larger than 0.65 mm<\/td><\/tr><tr><td><strong>Outlet and isolating valve<\/strong><\/td><td>Feeds the house; lets you shut off for repairs<\/td><td>Full-bore valve, 25 mm pipe<\/td><\/tr><tr><td><strong>Distribution pipework<\/strong><\/td><td>Carries water to each outlet<\/td><td>Continuous fall, few bends<\/td><\/tr><\/tbody><\/table><figcaption class=\"wp-element-caption\">Lid, screen and support points follow Water Regs UK guidance on cold water storage cisterns.<\/figcaption><\/figure>\n\n\n\n<p>The float valve and the overflow have their own guides: <a href=\"https:\/\/watertankcalculator.com\/guides\/what-is-a-float-valve-and-how-does-it-control-tank-filling\/\">what a float valve is and how it controls tank filling<\/a> and <a href=\"https:\/\/watertankcalculator.com\/guides\/water-tank-overflowing-what-causes-it-and-how-to-fix-it\/\">water tank overflowing<\/a>. Getting water up to the tank is a separate question from getting it down. Where mains pressure is too weak to reach the roof, the tank is filled by a pump from a ground-level tank, as explained in <a href=\"https:\/\/watertankcalculator.com\/guides\/overhead-vs-underground-water-tank-which-is-better\/\">overhead vs underground water tanks<\/a> and <a href=\"https:\/\/watertankcalculator.com\/guides\/why-is-my-water-tank-taking-so-long-to-refill\/\">why a water tank takes so long to refill<\/a>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Gravity feed or a pump?<\/h2>\n\n\n\n<figure class=\"wp-block-table is-style-stripes\"><table class=\"has-fixed-layout\"><thead><tr><th><\/th><th>Gravity feed<\/th><th>Pumped<\/th><\/tr><\/thead><tbody><tr><td><strong>Pressure<\/strong><\/td><td>Low; fixed by height<\/td><td>Whatever the pump is set to<\/td><\/tr><tr><td><strong>Power cuts<\/strong><\/td><td>Keeps working until the tank is empty<\/td><td>Stops once the pressure vessel is drawn down, unless there is backup power<\/td><\/tr><tr><td><strong>Running cost<\/strong><\/td><td>None for delivery<\/td><td>Electricity and servicing<\/td><\/tr><tr><td><strong>Noise and moving parts<\/strong><\/td><td>None<\/td><td>Pump, pressure switch, vessel<\/td><\/tr><tr><td><strong>Fittings<\/strong><\/td><td>Need low-pressure types<\/td><td>Any<\/td><\/tr><tr><td><strong>Best for<\/strong><\/td><td>Simple homes, unreliable power, lower floors<\/td><td>Top-floor bathrooms, mains-type appliances, large houses<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>Many homes use both: gravity for taps and toilets, and a small pump for the showers. <a href=\"https:\/\/watertankcalculator.com\/guides\/pump-system-vs-gravity-feed\/\">Pump system vs gravity feed<\/a> compares costs and performance, <a href=\"https:\/\/watertankcalculator.com\/guides\/what-is-a-pressure-tank-and-how-is-it-different-from-a-storage-tank\/\">what a pressure tank is<\/a> explains the vessel a pump needs, and the <a href=\"https:\/\/watertankcalculator.com\/calculators\/pressure\/pump-head-pressure-calculator\">Pump Head Pressure Calculator<\/a> sizes the head.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Mistakes to avoid<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Measuring head to the floor.<\/strong> Measure from the tank outlet to the shower head or tap itself. On the top floor the difference is most of your pressure.<\/li>\n\n\n\n<li><strong>Running a long feed in narrow pipe.<\/strong> A tank 6 m above a tap has 0.59 bar. Through 40 m of 15 mm pipe at 10 L\/min, friction takes 0.30 bar of it, which is half. The same run in 25 mm pipe loses 0.03 bar.<\/li>\n\n\n\n<li><strong>Buying a bigger tank to fix weak pressure.<\/strong> Volume changes how long the water lasts, not how hard it pushes.<\/li>\n\n\n\n<li><strong>Testing one tap and calling it done.<\/strong> Test the highest outlet, and test with a second outlet running.<\/li>\n\n\n\n<li><strong>Fitting mains-pressure shower heads and appliances.<\/strong> Many are built for 1.4 bar and up. Buy for the pressure you have.<\/li>\n\n\n\n<li><strong>Raising the tank without checking the roof.<\/strong> The extra height is cheap. The structure to carry it safely may not be.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">More calculators for a gravity-fed tank<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><a href=\"https:\/\/watertankcalculator.com\/calculators\/household\/water-tank-size-for-home-calculator\">Water Tank Size for Home Calculator<\/a>: the storage volume for your household and supply gap.<\/li>\n\n\n\n<li><a href=\"https:\/\/watertankcalculator.com\/calculators\/household\/how-long-will-my-tank-last-calculator\">How Long Will My Tank Last Calculator<\/a>: days of supply from the volume you have.<\/li>\n\n\n\n<li><a href=\"https:\/\/watertankcalculator.com\/calculators\/flow\/tank-refill-time-calculator\">Tank Refill Time Calculator<\/a>: how long the tank takes to fill at your inlet flow.<\/li>\n\n\n\n<li><a href=\"https:\/\/watertankcalculator.com\/calculators\/flow\/tank-drainage-time-calculator\">Tank Drainage Time Calculator<\/a>: how long a tank takes to empty by gravity through its outlet.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Frequently asked questions<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">What is the minimum height for a gravity-fed shower?<\/h3>\n\n\n\n<p>About 1 m between the base of the tank and the shower head, which gives 0.1 bar, the minimum that gravity shower fittings are rated for. That is enough to work with a low-pressure head but not to impress. Around 3 m gives a workable shower and around 5 m a comfortable one. Add height or pipe size if the run is long.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Can I run a washing machine off a gravity-feed tank?<\/h3>\n\n\n\n<p>Yes, if the machine is rated for it. Minimum inlet pressures range from 0.2 bar on some top-loaders, which is 2 m of head, to 1.4 bar on others, which is 14 m. The figure is in the technical data section of the manual. Check it before buying, and choose a low-pressure model for a tank-fed home.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Why does my tap run fine but the shower is weak?<\/h3>\n\n\n\n<p>Because the shower head is higher than the tap. A tap 2 m below the tank gets 0.2 bar. A shower head 1.5 m above that tap is only 0.5 m below the tank and gets 0.05 bar. In a gravity system the height of the outlet matters as much as the height of the tank.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Does a bigger tank give more pressure?<\/h3>\n\n\n\n<p>No. Pressure depends only on the height of the water surface above the outlet. A 500 L tank and a 5,000 L tank at the same height give the same pressure. A bigger tank lasts longer between refills, and that is all.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Does tank shape affect pressure?<\/h3>\n\n\n\n<p>Slightly, through the water level. Take two 1,000 L tanks on the same base. A tall one 0.8 m across holds 2 m of water when full, so it gives 0.2 bar more than its base level, but the level falls 20 cm for every 100 L used. A wide one 1.6 m across holds only 0.5 m of water, and its level falls 5 cm per 100 L. The tall tank gives more pressure at every fill level; the wide tank gives steadier pressure. <a href=\"https:\/\/watertankcalculator.com\/guides\/round-vs-rectangular-water-tank\/\">Round vs rectangular water tanks<\/a> covers the other trade-offs of shape.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">What pipe size should I use for a gravity-feed system?<\/h3>\n\n\n\n<p>Use 25 mm internal diameter for the main feed from the tank, and step down to 15 or 20 mm only at the last branch to each outlet. With 5 m of head and 20 m of pipe, 25 mm pipe keeps 0.45 bar at the outlet while a shower and a tap run together. The same flow through 15 mm pipe leaves 0.04 bar. Go larger still on runs much longer than 20 m.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Does a gravity-feed system work in a power cut?<\/h3>\n\n\n\n<p>Yes. Delivery needs no electricity, so water flows for as long as there is water in the tank. If the tank is refilled by a pump, it will not refill until the power returns, so the stored volume decides how long you can go. If the whole system feels weak in normal use, see <a href=\"https:\/\/watertankcalculator.com\/guides\/my-water-tank-pressure-is-low\/\">my water tank pressure is low<\/a>.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Sources<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Mira Showers, <a href=\"https:\/\/www.mirashowers.co.uk\/support\/help-and-faq\/what-water-supply-do-i-have-low-pressure-gravity-system\" target=\"_blank\" rel=\"noreferrer noopener\">Low pressure gravity system<\/a> and <a href=\"https:\/\/resources.kohler.com\/plumbing\/mira\/pdf\/1095475-w2-mira-energise-and-l10-shower-fittings-guide.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">shower fittings guide<\/a>. Cistern base at least 1 m above the showerhead; minimum maintained pressure 0.1 bar.<\/li>\n\n\n\n<li>Bosch, top-loading washing machine manuals: <a href=\"https:\/\/media3.bosch-home.com\/Documents\/9001792021_A.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">ExpertCare<\/a> (20 kPa to 1,000 kPa) and <a href=\"https:\/\/media3.bosch-home.com\/Documents\/9001345015_A.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">C series<\/a> (30 kPa to 800 kPa).<\/li>\n\n\n\n<li>Samsung, <a href=\"https:\/\/www.samsung.com\/hk_en\/support\/home-appliances\/what-range-should-the-water-pressure-be-for-samsung-washing-machine\" target=\"_blank\" rel=\"noreferrer noopener\">What range should the water pressure be for a Samsung washing machine?<\/a> Between 20 and 116 psi.<\/li>\n\n\n\n<li>Corcos G, <a href=\"https:\/\/bdd.pseau.org\/outils\/ouvrages\/aplv_air_in_pipes_manual_en.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">Air in Water Pipes<\/a>, 2nd edition, Agua Para La Vida, 2003. Air pockets at high points in gravity-flow pipelines.<\/li>\n\n\n\n<li>Water Regs UK, <a href=\"https:\/\/wras.co.uk\/downloads\/public_area\/guidance\/publications\/general\/april_2023\/guidance_2024\/booklets\/cold_water_storage_cisterns_feb_2024_v_1.1.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">Cold water storage cisterns<\/a> (February 2024). Lid, overflow screen, support and insulation.<\/li>\n\n\n\n<li>Brad Lancaster, <a href=\"https:\/\/www.harvestingrainwater.com\/rainwater-harvesting-inforesources\/suppliers\/full-port-valves-for-gravity-fed-tankscisterns\/\" target=\"_blank\" rel=\"noreferrer noopener\">Full-port valves for gravity-fed tanks and cisterns<\/a>, Rainwater Harvesting for Drylands and Beyond.<\/li>\n\n\n\n<li>WaterSafe (UK), <a href=\"https:\/\/www.watersafe.org.uk\/advice\/common_plumbing_questions1\/pressure\/what_is_the_minimum_water_pressure_that_a_water_supplier_must_supply\/\" target=\"_blank\" rel=\"noreferrer noopener\">minimum water pressure a supplier must provide<\/a>. 10 m head target at the boundary.<\/li>\n\n\n\n<li>US EPA, <a href=\"https:\/\/www.epa.gov\/sites\/production\/files\/2018-07\/documents\/ws-products-specification-showerheads-v1-1.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">WaterSense Specification for Showerheads, version 1.1<\/a>. Lowest test pressure 20 psi.<\/li>\n\n\n\n<li>NIST, <a href=\"https:\/\/www.nist.gov\/pml\/special-publication-811\" target=\"_blank\" rel=\"noreferrer noopener\">Special Publication 811<\/a>. 1 m of water head is about 9.81 kPa (0.098 bar, 1.42 psi).<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>A gravity-feed water system uses height in place of a pump. The tank sits above the taps, and the weight of the water in the pipe pushes it out when a tap opens. Every metre of height between the water surface and the tap gives about 0.1 bar (1.42 psi) of pressure, so a tank [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":77,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[],"class_list":["post-122","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-concepts-explainers"],"_links":{"self":[{"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/posts\/122","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/comments?post=122"}],"version-history":[{"count":2,"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/posts\/122\/revisions"}],"predecessor-version":[{"id":474,"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/posts\/122\/revisions\/474"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/media\/77"}],"wp:attachment":[{"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/media?parent=122"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/categories?post=122"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/tags?post=122"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}