If your Estonian property has no mains sewerage, “holding tank vs septic tank” looks like a product choice. It is really a site question: the law, your municipality, the groundwater under the plot and the way you use the house usually rule out one or two of the three systems before you open a brochure. A holding tank only stores wastewater until a tanker collects it; a septic tank system and a biological treatment plant treat wastewater on site and release the effluent. Below: the three working principles, what Estonian rules and your plot allow, what each system costs to run \u2014 with no invented prices \u2014 and five questions that lead to the right system.<\/p>\n
Sewage holding tank<\/strong> (reoveemahuti<\/em>; in legal texts reovee kogumismahuti<\/em>; UK readers may know a sealed tank as a cesspool or cesspit). A sealed underground tank with an inlet and no outlet. Nothing is treated: a tanker pumps everything out and drives it to a reception point (purgimiss\u00f5lm<\/em>) \u2014 a service called purgimine<\/em>. The ministry’s 2015 guide to on-site wastewater systems says that, as no treatment takes place, there must be no outflow and no uncontrolled leaks. Saaremaa municipality’s on-site wastewater rules \u2014 one example of a municipal eeskiri<\/em> \u2014 define it as a “pealt suletav lekkekindel \u00e4ravooluta rajatis”: a covered, leak-tight structure without an outlet.<\/p>\n Septic tank<\/strong> (septik<\/em>) with an infiltration field<\/strong> (imbv\u00e4ljak<\/em>). The tank is only the first stage: solids settle and fats float (mechanical treatment), and the water flows on \u2014 the Saaremaa definition ends “sellel on v\u00e4ljavool”, it has an outlet. Perforated pipes spread it through a gravel or sand bed, where soil micro-organisms do the biological part before it seeps towards the groundwater. A septic tank without a working field is not a treatment system.<\/p>\n Biological treatment plant<\/strong> (biopuhasti<\/em>). A factory-made unit with a settling chamber, a biofilm or aerated activated-sludge stage and a final settler. It needs electricity, and the treated effluent still has to go somewhere: soil, a ditch or a water body. In law both this and the septic system are an own treatment plant (omapuhasti<\/em>).<\/p>\n The Water Act.<\/strong> Veeseadus<\/em> \u00a7 124 sorts plots by sewage collection area (reoveekogumisala<\/em>), sized in population equivalents (p.e.): in an area of 2,000 p.e. or more without public sewerage, own treatment plants are prohibited and the lawful route is a leak-tight holding tank emptied to the municipality’s reception point (\u00a7 124(2), (4)). In a smaller collection area, or outside one, an own treatment plant may also be allowed (\u00a7 124(3), (6)). For the technology choice one detail matters: below 2,000 p.e. the Act speaks of a plant discharging biologically or advanced-treated effluent \u2014 wording that a septic tank with infiltration alone does not match.<\/p>\n Your municipality.<\/strong> Every municipality (kohalik omavalitsus<\/em>) adopts rules for on-site wastewater treatment and removal (reovee kohtk\u00e4itluse ja \u00e4raveo eeskiri<\/em>, \u00a7 104(7)), and they can be stricter than the Act. Example only: Saaremaa requires holding tanks in densely built places outside collection areas, such as summer-house cooperatives, where the required distance from wells cannot be kept. Read your own municipality’s rules; how to check whether your plot lies in a collection area, where to find the local rules and whom to ask is mapped in wastewater options for a home without mains sewerage<\/a>.<\/p>\n Groundwater and soil.<\/strong> Regulation No 61 of the Minister of the Environment (\u00a7 8) allows effluent to be infiltrated into the soil only where leading it to a distant water body or ditch is not economically justified and groundwater is not put at risk, and then in quantities set by groundwater protection class:<\/p>\nWhat do your plot and municipality allow?<\/h2>\n