{"id":39598,"date":"2026-09-17T20:16:29","date_gmt":"2026-09-17T17:16:29","guid":{"rendered":"https:\/\/reoveemahutid.ee\/?p=39598"},"modified":"2026-09-17T20:19:30","modified_gmt":"2026-09-17T17:19:30","slug":"what-size-holding-tank","status":"publish","type":"post","link":"https:\/\/reoveemahutid.ee\/en\/what-size-holding-tank\/","title":{"rendered":"What size sewage holding tank do you need? A water-use calculation"},"content":{"rendered":"<p>A sewage holding tank (Estonian <em>reoveemahuti<\/em>; in legal texts <em>reovee kogumismahuti<\/em>; UK readers may know a sealed tank as a cesspool or cesspit) only stores wastewater until a tanker pumps it out. There is no treatment and no outlet, so everything that goes down your drains must be driven away. &#8220;What size holding tank do I need?&#8221; therefore depends on two things: how much water your household uses and how often you are prepared to pay for a tanker. The short answer: people \u00d7 litres per day \u00d7 days between emptyings, plus a reserve, capped by the tankers working in your area. Below are the formula, its assumptions, worked examples and the matching Vesmaco volumes from 2 to 15 m\u00b3.<\/p>\n<h2>Start from your own water-meter readings<\/h2>\n<p>Almost every litre that passes your water meter ends up in the holding tank, so the meter beats any rule of thumb.<\/p>\n<ol>\n<li>Take one month&#8217;s consumption from your water bill, or note the meter reading (m\u00b3) on two dates about a month apart.<\/li>\n<li>Convert it: <code>litres per day = m\u00b3 used \u00d7 1,000 \u00f7 number of days<\/code>.<\/li>\n<li>If use varies through the year, work with the busiest month, not the annual average.<\/li>\n<li>Subtract water that never reaches the drains (garden watering) only if you can estimate it; otherwise keep it as a margin.<\/li>\n<\/ol>\n<p>Illustration only: 9.6 m\u00b3 in 30 days is 320 L per day; for three people, about 107 L per person per day.<\/p>\n<p>No meter yet \u2014 a new build, or a private well without one? Use the official planning range: the Estonian ministry&#8217;s guide to on-site wastewater systems (2015) plans for <strong>100\u2013150 L of wastewater per resident per day<\/strong>. Calculate with both ends of the range and switch to real readings as soon as you can \u2014 your own meter data takes precedence.<\/p>\n<p>This is also why rules of thumb found online disagree. &#8220;So many cubic metres per person per month&#8221; is the same arithmetic with hidden assumptions (100\u2013150 L a day equals 3\u20134.5 m\u00b3 per person a month), and &#8220;a house needs 10\u201315 m\u00b3&#8221; ignores how many people live there and how often the tanker comes.<\/p>\n<h2>The formula and its assumptions<\/h2>\n<pre><code>required volume (L) = persons \u00d7 litres per person per day \u00d7 (target days between emptyings + reserve days)<\/code><\/pre>\n<p>Check any tank size with the same formula turned round:<\/p>\n<pre><code>days between emptyings = usable volume (L) \u00f7 (persons \u00d7 litres per person per day)\nemptyings per year     = 365 \u00d7 occupancy share \u00f7 days between emptyings<\/code><\/pre>\n<p>Every input is a visible assumption:<\/p>\n<ul>\n<li><strong>Litres per person per day<\/strong> \u2014 your meter figure, or the 100\u2013150 L planning range.<\/li>\n<li><strong>Target days between emptyings<\/strong> \u2014 your choice: a larger tank costs more to buy and bury, a smaller one means more tanker visits. Yearly desludging figures quoted for septic tanks describe sludge removal from a different kind of system and must not be used here.<\/li>\n<li><strong>Reserve days<\/strong> \u2014 the time between ordering the tanker and its arrival; ask your local emptying company. The ministry guide says a holding tank must never overflow and, for dipstick checks, advises ordering when the level passes about half the diameter. With a level alarm, the reserve is the volume above the sensor; on the wireless alarm offered with Vesmaco tanks, the sensor cable length sets the alarm level.<\/li>\n<li><strong>Usable volume<\/strong> \u2014 the examples below treat usable volume as equal to nominal volume for simplicity. In reality the alarm level leaves part of the tank as reserve, so the usable volume is somewhat below the nominal volume and real intervals are somewhat shorter. For an exact figure, check the drawing for your model and the alarm height you set.<\/li>\n<li><strong>Occupancy share<\/strong> \u2014 1 for a permanent home; for a seasonal one, the fraction of the year in use.<\/li>\n<li><strong>Only household wastewater enters the tank.<\/strong> Rainwater, drainage water and groundwater are not in the formula and must be kept out.<\/li>\n<\/ul>\n<h3>One legal minimum to check<\/h3>\n<p>In one situation the law sets a floor. Under the Public Water Supply and Sewerage Act (\u00dcVVKS) \u00a7 47, if your property lies in a sewage collection area (<em>reoveekogumisala<\/em>) of 2000 population equivalents or more and cannot connect because public sewerage is missing, you must install a leak-tight holding tank <strong>large enough to hold at least two weeks&#8217; wastewater<\/strong> (\u00a7 47(7)). In return the water company must organise the emptying service (<em>purgimisteenus<\/em>) at your request, and you are entitled to it twice per calendar month (\u00a7 47(10)). On planning figures, two weeks for four people means 5.6\u20138.4 m\u00b3.<\/p>\n<p>This rule covers that situation only. Elsewhere, look in your municipality&#8217;s rules on on-site wastewater treatment and removal (<em>reovee kohtk\u00e4itluse ja \u00e4raveo eeskiri<\/em>, Water Act \u00a7 104(7)) \u2014 check your own municipality before you order.<\/p>\n<h2>Worked examples: 2, 4 and 6 people<\/h2>\n<p>Assumptions for both tables: permanent occupancy, 100\u2013150 L per person per day, nominal volume, no reserve days added yet.<\/p>\n<p><strong>Volume needed for a chosen interval<\/strong><\/p>\n<figure class=\"wp-block-table\">\n<table>\n<thead>\n<tr>\n<th>Household<\/th>\n<th>Daily wastewater<\/th>\n<th>Every 7 days<\/th>\n<th>Every 14 days<\/th>\n<th>Every 28 days<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>2 people<\/td>\n<td>200\u2013300 L<\/td>\n<td>1.4\u20132.1 m\u00b3<\/td>\n<td>2.8\u20134.2 m\u00b3<\/td>\n<td>5.6\u20138.4 m\u00b3<\/td>\n<\/tr>\n<tr>\n<td>4 people<\/td>\n<td>400\u2013600 L<\/td>\n<td>2.8\u20134.2 m\u00b3<\/td>\n<td>5.6\u20138.4 m\u00b3<\/td>\n<td>11.2\u201316.8 m\u00b3<\/td>\n<\/tr>\n<tr>\n<td>6 people<\/td>\n<td>600\u2013900 L<\/td>\n<td>4.2\u20136.3 m\u00b3<\/td>\n<td>8.4\u201312.6 m\u00b3<\/td>\n<td>16.8\u201325.2 m\u00b3<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/figure>\n<p><strong>How long a given tank lasts<\/strong><\/p>\n<figure class=\"wp-block-table\">\n<table>\n<thead>\n<tr>\n<th>Tank (nominal)<\/th>\n<th>2 people<\/th>\n<th>4 people<\/th>\n<th>6 people<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>3 m\u00b3<\/td>\n<td>10\u201315 days<\/td>\n<td>5\u20137.5 days<\/td>\n<td>3.3\u20135 days<\/td>\n<\/tr>\n<tr>\n<td>5 m\u00b3<\/td>\n<td>17\u201325 days<\/td>\n<td>8\u201312.5 days<\/td>\n<td>5.5\u20138 days<\/td>\n<\/tr>\n<tr>\n<td>10 m\u00b3<\/td>\n<td>33\u201350 days<\/td>\n<td>17\u201325 days<\/td>\n<td>11\u201317 days<\/td>\n<\/tr>\n<tr>\n<td>15 m\u00b3<\/td>\n<td>50\u201375 days<\/td>\n<td>25\u201337 days<\/td>\n<td>17\u201325 days<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/figure>\n<p>Step by step for a family of four wanting the tanker about every two weeks:<\/p>\n<ol>\n<li>Daily wastewater: 4 \u00d7 100\u2013150 L = 400\u2013600 L.<\/li>\n<li>Fourteen days: 5,600\u20138,400 L.<\/li>\n<li>Reserve, assuming the tanker comes within three days of your call (ask your company): 3 \u00d7 400\u2013600 L = 1,200\u20131,800 L.<\/li>\n<li>Required volume: 6,800\u201310,200 L. Rounded up to the next volume in the Vesmaco range, that is 7 m\u00b3 at 100 L per person and 12 m\u00b3 at 150 L. Meter data narrows this: at a measured 110 L per person, 4 \u00d7 110 \u00d7 17 = 7,480 L, so 8 m\u00b3.<\/li>\n<\/ol>\n<p>The official benchmark fits the formula: the ministry guide gives at least 5 m\u00b3 as the optimal size for a four-person family living permanently, emptied about once a week. By the formula, 5 m\u00b3 lasts 8\u201312.5 days at nominal volume \u2014 roughly weekly once you order before the tank is full.<\/p>\n<p>The drawback, stated plainly: emptying is the running cost of a holding tank. Four people with 5 m\u00b3 need about 29\u201344 tanker visits a year; with 10 m\u00b3, about 15\u201322. Budget with <code>annual cost = emptyings per year \u00d7 your local price per visit<\/code>. Intervals are covered in <a href=\"\/en\/how-often-empty-holding-tank\/\">how often a sewage holding tank should be emptied<\/a>.<\/p>\n<h2>Tanker capacity sets a practical upper limit<\/h2>\n<p>A tank that holds more than the tanker cannot be emptied in one visit. The ministry guide (2015) says small tankers (<em>paakauto<\/em>) carry 4\u20135 m\u00b3 and the largest about 10 m\u00b3, and advises checking what is available locally.<\/p>\n<p>Before fixing the size, ask two or three emptying companies serving your address:<\/p>\n<ul>\n<li>what load their vehicle takes in one visit;<\/li>\n<li>whether they charge per visit or per cubic metre, and what a second load costs;<\/li>\n<li>their usual notice time \u2014 your reserve days.<\/li>\n<\/ul>\n<p>Then apply the cap: choose the smaller of your calculated volume and the largest single load available locally, unless you knowingly accept two loads per emptying. Where \u00dcVVKS \u00a7 47 applies, its two-week minimum still comes first. Six people wanting a 28-day interval would need 16.8\u201325.2 m\u00b3 \u2014 beyond any single tanker and the 15 m\u00b3 top of Vesmaco&#8217;s range. If a tanker of about 10 m\u00b3 serves your area, the realistic plan is 10 m\u00b3 emptied every 11\u201317 days.<\/p>\n<h2>Permanent, seasonal or rental use: how the pattern changes the result<\/h2>\n<p><strong>Permanent home.<\/strong> Occupancy share is 1; size for a busy month. Intervals are short, so there is little slack \u2014 the ministry guide calls a level sensor advisable.<\/p>\n<p><strong>Summer house or weekend use.<\/strong> Size for the period of use; an annual average would mislead. Four people staying two days a week produce 800\u20131,200 L a week, so 3 m\u00b3 lasts about 2.5\u20133.75 weeks and 5 m\u00b3 about 4\u20136. The occupancy share gives the yearly count: 40 days of use a year with a 5 m\u00b3 tank means 40 \u00f7 8\u201312.5 = 3\u20135 emptyings. When the smallest models are genuinely enough is covered in <a href=\"\/en\/small-holding-tank-2-3m3\/\">2\u20133 m\u00b3 sewage holding tanks<\/a>.<\/p>\n<p><strong>Holiday rental or campsite.<\/strong> Size for the peak: guests at full occupancy \u00d7 litres \u00d7 nights between tanker visits. Eight guests produce 800\u20131,200 L a day on planning figures, so 10 m\u00b3 lasts 8\u201312.5 days when fully booked. The planning range was written for residents, so prefer meter readings from your busiest weeks.<\/p>\n<h2>From result to model: Vesmaco tanks 2\u201315 m\u00b3<\/h2>\n<p>Round your result <strong>up<\/strong> to the next volume in the range. Vesmaco manufactures 19 horizontal reinforced-fibreglass (GRP) holding tanks:<\/p>\n<figure class=\"wp-block-table\">\n<table>\n<thead>\n<tr>\n<th>Volume<\/th>\n<th>Diameter families available<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>2 m\u00b3, 3 m\u00b3<\/td>\n<td>D1100<\/td>\n<\/tr>\n<tr>\n<td>4 m\u00b3, 5 m\u00b3<\/td>\n<td>D1100 or D1400<\/td>\n<\/tr>\n<tr>\n<td>6, 7, 8, 9, 10 m\u00b3<\/td>\n<td>D1400 or D1600<\/td>\n<\/tr>\n<tr>\n<td>12 m\u00b3<\/td>\n<td>D1600<\/td>\n<\/tr>\n<tr>\n<td>15 m\u00b3<\/td>\n<td>D1600 or D2000<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/figure>\n<p>Where a volume comes in two diameters, the larger one gives a shorter tank but a deeper excavation. Dimensions, weights and drawings are in the <a href=\"\/en\/#mudelidjajoonised\">model table<\/a>; choosing a diameter for your plot is explained in <a href=\"\/en\/holding-tank-dimensions-drawings\/\">holding tank dimensions and drawings<\/a>. If your result falls between the two most common sizes, see <a href=\"\/en\/5m3-or-10m3-holding-tank\/\">5 m\u00b3 or 10 m\u00b3: which size should you choose?<\/a><\/p>\n<h2>Frequently asked questions<\/h2>\n<p><strong>How much wastewater does one person produce per day?<\/strong> The ministry&#8217;s 2015 guide plans for 100\u2013150 L per resident per day. It is a planning range, not a measurement: your own water-meter readings take precedence.<\/p>\n<p><strong>Is 5 m\u00b3 enough for a family of four?<\/strong> As a minimum, yes \u2014 if you accept roughly weekly emptying; that is the ministry guide&#8217;s benchmark. For a tanker every two weeks the same family needs about 7\u201312 m\u00b3 including a reserve, depending on its measured water use. On planning figures 5 m\u00b3 holds less than two weeks&#8217; wastewater for four people, which matters where \u00dcVVKS \u00a7 47(7) applies.<\/p>\n<p><strong>Is a bigger tank always better?<\/strong> No. The yearly volume of wastewater stays the same; a bigger tank only divides it into fewer visits. That helps where the local price is per visit and the tanker can take the whole load. Where the charge is per cubic metre \u2014 as under \u00dcVVKS \u00a7 48(2) \u2014 tank size does not change the bill. A bigger tank is also longer or deeper to bury.<\/p>\n<hr \/>\n<p><strong>Send us your calculation.<\/strong> Put your numbers \u2014 people, litres per day and their source, the interval you want, reserve days and the largest tanker load available locally \u2014 into the <a href=\"\/en\/#order\">quote form<\/a> or call <strong>+372 641 8550<\/strong>, and we will suggest matching Vesmaco models with their drawings. Vesmaco manufactures and delivers the tanks; installation is done by your installer and emptying by your local emptying company.<\/p>\n<h2>Sources<\/h2>\n<ul>\n<li>Ministry of the Environment (2015), <em>Juhendmaterjal hajaasustuse reoveek\u00e4itluss\u00fcsteemide kavandamiseks, valikuks, ehitamiseks ja hooldamiseks<\/em> \u2014 planning figures, four-person benchmark, tanker sizes, operating advice (in Estonian): <a href=\"https:\/\/kliimaministeerium.ee\/sites\/default\/files\/documents\/2021-10\/Juhendmaterjal%20hajaasustuse%20reoveek%C3%A4itluss%C3%BCsteemide%20kavandamiseks,%20valikuks,%20ehitamiseks%20ja%20hooldamiseks.pdf\" target=\"_blank\" rel=\"noopener\">kliimaministeerium.ee (PDF)<\/a><\/li>\n<li>Public Water Supply and Sewerage Act (<em>\u00dchisveev\u00e4rgi ja -kanalisatsiooni seadus<\/em>, \u00dcVVKS), \u00a7 47 and \u00a7 48(2): <a href=\"https:\/\/www.riigiteataja.ee\/akt\/\u00dcVVKS\" target=\"_blank\" rel=\"noopener\">Riigi Teataja, Estonian text<\/a> \u00b7 <a href=\"https:\/\/www.riigiteataja.ee\/en\/eli\/512092025001\/consolide\" target=\"_blank\" rel=\"noopener\">official English translation<\/a><\/li>\n<li>Water Act (<em>Veeseadus<\/em>), \u00a7 104(7): <a href=\"https:\/\/www.riigiteataja.ee\/akt\/122022019001?leiaKehtiv\" target=\"_blank\" rel=\"noopener\">Riigi Teataja, Estonian text<\/a> \u00b7 <a href=\"https:\/\/www.riigiteataja.ee\/en\/eli\/509092026003\/consolide\" target=\"_blank\" rel=\"noopener\">official English translation<\/a><\/li>\n<li>The English translations are provided for information; only the Estonian text has legal force.<\/li>\n<li>Vesmaco model table and drawings: <a href=\"https:\/\/reoveemahutid.ee\/en\/#mudelidjajoonised\">reoveemahutid.ee\/en\/<\/a><\/li>\n<li>Smartel Tank-Check RF-431 wireless level alarm, manufacturer sheet: <a href=\"https:\/\/smartel.vesmaco.eu\" target=\"_blank\" rel=\"noopener\">smartel.vesmaco.eu<\/a><\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Work out holding tank size from real water use: people \u00d7 litres per day \u00d7 days between emptying. Worked examples for 2\u201315 m\u00b3 tanks, assumptions explained.<\/p>\n","protected":false},"author":28,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[],"tags":[],"class_list":["post-39598","post","type-post","status-publish","format-standard","hentry"],"acf":[],"_links":{"self":[{"href":"https:\/\/reoveemahutid.ee\/en\/wp-json\/wp\/v2\/posts\/39598","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/reoveemahutid.ee\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/reoveemahutid.ee\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/reoveemahutid.ee\/en\/wp-json\/wp\/v2\/users\/28"}],"replies":[{"embeddable":true,"href":"https:\/\/reoveemahutid.ee\/en\/wp-json\/wp\/v2\/comments?post=39598"}],"version-history":[{"count":2,"href":"https:\/\/reoveemahutid.ee\/en\/wp-json\/wp\/v2\/posts\/39598\/revisions"}],"predecessor-version":[{"id":39839,"href":"https:\/\/reoveemahutid.ee\/en\/wp-json\/wp\/v2\/posts\/39598\/revisions\/39839"}],"wp:attachment":[{"href":"https:\/\/reoveemahutid.ee\/en\/wp-json\/wp\/v2\/media?parent=39598"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/reoveemahutid.ee\/en\/wp-json\/wp\/v2\/categories?post=39598"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/reoveemahutid.ee\/en\/wp-json\/wp\/v2\/tags?post=39598"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}