Stages of purification
The number of purification stages provided for in the filter design. At each stage, water passes through its own filter element, clearing itself of certain contaminants; in this case, the steps are arranged in order from coarser cleaning to finer. For example,
a three-stage system may look like this: the first stage is mechanical removal of impurities, the second stage is the removal of ferrous, and the third is filtration through a carbon cartridge.
The more stages of purification — the more advanced the filter is considered, the cleaner water it usually provides at the outlet. Accordingly, this moment largely depends on the purpose (see “Type”): for example, multi-stage filtration is quite rare in main models, it is practically not used at all in pre-filters, but the number of stages can reach 9 in models for sink.
Filtration speed
The amount of water that the filter is able to pass through itself per unit of time (of course, effectively purified in the process); usually stated in liters per minute. This parameter is largely related to the type (see above): for example, in jugs, the filtration rate usually does not exceed 0.5 L per minute, while for main devices that supply entire apartments, a throughput of tens or even hundreds of liters is required.
Note that it does not always make sense to pursue a high filtration rate. After all, other things being equal, finer cleaning takes more time; accordingly, the faster the filter works, the higher the chance that the quality of such cleaning will be relatively low. And devices that purify water efficiently and quickly usually have an appropriate price. Therefore, it is worth considering the purpose of the filter and, on the basis of this, determine the balance between the filtration speed and its quality when choosing. It is also worth keeping in mind the conditions of use: for example, if you need to filter low-quality tap water for drinking, it is better to sacrifice speed in favor of efficiency.
Replacement cartridges
Models of replaceable cartridges for which the filter is designed. Knowing the names of models, it will be much easier for you to find a replacement for an exhausted cartridge. In addition, the options directly named by the manufacturer are fully compatible with the filter and correspond to official specifications, while there is no such guarantee for "non-native" cartridges.
Several names in this paragraph are usually indicated for filters with multi-stage filtration (see "Stages of purification") — a cartridge for each stage.
Tank
Availability of a
tank in the reverse osmosis system. It provides a convenient and necessary reserve of clean water (since the filtration process itself is slow) and is installed after the membrane, before the final purification stage (post-filter). Inside the tank, there is a pressurized air compartment that allows water to be displaced when the faucet is opened. That is why the useful volume of the tank is less than the total volume, which we indicate.
The volume (size) of the reverse osmosis tank is selected based on needs and available space. The most common option is
12 liters, suitable for a family of 3–4 people.