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WaterAI · Calculation and Selection
Water treatment capacity calculation starts by bringing the catalogue's four separate units onto a single axis: GPD, tonnes/day, m³/hour and litres/hour show the same unit at different sizes. The six tables below give that conversion, the tank volume by household size, the fill time of the tank, the difference between pumped and unpumped systems, and the softener resin calculation, all in figures. WaterAI runs the same calculation on the values you give it.
WaterAI Assistant
In six questions it takes where you will use it, your water source and your daily consumption, compares them against the capacity data of the units in the catalogue and ranks the ones that suit you. At the end you see not just products but how that result was reached.
About 1 minute · no sign-up needed
How many litres is 300 GPD?
1,136 litres / day
1 US gallon = 3.785 litres
How many minutes does an 8 litre tank take to fill?
8 min – 9 min with a pumped 300 GPD
With an unpumped 50 GPD it takes up to an hour
Resin for a four-person household?
14 litres of resin
35 °Fr hardness, regeneration every 4 days
Table 1
Capacity is written in four separate units in the catalogue, and that makes comparing two units impossible. The table below brings them all onto the litres/day axis; the assistant makes exactly this conversion.
| What the label says | Litres / day | Litres / hour | Where it is used in practice |
|---|---|---|---|
| 50 GPD | 189 | 8 | Under-sink without pump — low output |
| 100 GPD | 379 | 16 | Under-sink without pump — the common class |
| 300 GPD | 1,136 | 47 | Domestic with pump — the entry class in the catalogue |
| 500 GPD | 1,893 | 79 | With pump, home / small office |
| 1,000 GPD | 3,785 | 158 | Office, café, small business |
| 2 Tonnes/Day | 2,000 | 83 | Cabinet softener, flat and villa |
| 5 Tonnes/Day | 5,000 | 208 | Villa, apartment block inlet, business |
| 10 Tonnes/Day | 10,000 | 417 | Estate inlet, hotel, production |
| 250 L/Hour | 6,000 | 250 | Hourly flow — multiplied by 24 |
| 1 m³/Hour | 24,000 | 1,000 | Process and industrial inlet |
| 8 m³/Hour | 192,000 | 8,000 | Plant scale |
Conversion factors: 1 GPD = 3.785 litres/day · 1 tonne/day = 1,000 litres/day · 1 m³/hour = 24,000 litres/day · 1 litre/hour = 24 litres/day.
Table 2
On a domestic unit the limit you feel is not the daily output but the water standing ready when you open the tap. Even the smallest domestic unit in the catalogue produces 1,136 litres a day; a family of four uses 12 litres for drinking and cooking. The comparison is therefore made on the tank axis.
| Household | Drinking + cooking water | Storage tank | Build |
|---|---|---|---|
| 1–2 people | 6 L/day | 8 litres | An under-sink system with a tank is enough. |
| 3–4 people | 12 L/day | 12 litres | A system with a tank; a pumped model under heavy use. |
| 5–6 people | 18 L/day | 12 litres | A pumped, high-output membrane is essential; the tank empties often. |
| 7 people and over | 21 L/day | No tank | A direct-flow system is the right answer — there is no waiting for a tank to fill. |
Assumption used
Drinking and cooking water is taken as 3 litres/day per person, and household water as 150 litres/day per person. These are planning values; if your consumption is different, you can enter your own figure in the assistant.
Table 3
The calculation has two steps: the daily output is divided by 24 to give the hourly output, then the usable volume of the tank is divided by that value. The usable volume is not the whole of the nominal figure — the air cushion inside the tank takes up room.
Fill time
Time (hours) = Usable volume (L) ÷ ( Daily output (L) ÷ 24 )
The usable volume is roughly %62 of the nominal tank volume. The ratio varies with the pre-charge pressure of the tank (0.5–0.7 bar) and the pressure on the line.
| Membrane | Output | 8 L tank (≈ 5 L usable) | 12 L tank (≈ 7.4 L usable) | ||
|---|---|---|---|---|---|
| Theoretical | Realistic | Theoretical | Realistic | ||
| 50 GPD unpumped | 189 L/day 7.9 L/saat | 40 min | 1 hr – 1 hr 30 min | 55 min | 1 hr 30 min – 2 hr 15 min |
| 100 GPD unpumped | 379 L/day 15.8 L/saat | 19 min | 30 min – 45 min | 30 min | 45 min – 1 hr 15 min |
| 300 GPD pumped | 1,136 L/day 47.3 L/saat | 6 min | 8 min – 9 min | 9 min | 11 min – 14 min |
| 400 GPD pumped | 1,514 L/day 63.1 L/saat | 5 min | 6 min – 7 min | 7 min | 8 min – 11 min |
Why the real time runs over the theoretical
As the tank fills, the back pressure inside it rises, the net pressure driving the membrane falls and output slows; the last litres take noticeably longer than the first. The label values of membranes are given for 4.1 bar and 25 °C — in winter the mains supply is around 10–15 °C, and cold water passes through the membrane more slowly. The third factor is ageing: output falls as the hours mount up.
The deviation is greater on an unpumped system, because there is nothing to make up the pressure lost. On a pumped system the pump holds the pressure steady, so the deviation is narrow.
Table 4
The difference comes down to a single thing: where the pressure driving the membrane comes from. An unpumped unit uses mains pressure alone; a pumped unit produces the missing pressure itself. Every other difference follows from that one.
| Criterion | Without pump | With pump |
|---|---|---|
| Mains pressure needed to work | At least 3 bar. Below that, output falls quickly. | 1.5 bar is enough — the pump makes up the missing pressure. |
| Typical membrane class | 50 – 100 GPD | 300 – 400 GPD |
| Fill time for an 8 litre tank | 30 minutes – 1.5 hours | 6 – 9 minutes |
| Reject water ratio | Rises as pressure falls; efficiency varies. | More predictable, because it works at constant pressure. |
| Electricity | Not needed. | Needed — access to a socket has to be planned. |
| Noise | Silent. | Audible while the pump runs; it stops once the tank is full. |
| Upper floors and low-pressure lines | Risky — the unit cannot deliver the output on its label. | Suitable; this is exactly the problem it was built for. |
A short decision rule
If you do not know the pressure at your tap, have it measured. Above 3 bar, an unpumped unit runs silently and without electricity. Below 3 bar, or on the upper floors of a building, choose a pumped model; otherwise the unit will never deliver the output on its label and will be taken for faulty.
Table 5
What sets the capacity of a softener is the amount of limescale the resin can hold. The calculation comes down to a one-line formula with three inputs: daily water consumption, the hardness of the water and the number of days between regenerations.
Resin volume
Resin (L) = Daily consumption (m³) × Hardness (°Fr) × Regeneration interval (days) ÷ 6
The 6 in the divisor is not arbitrary: 1 litre of standard cationic resin holds about 60 grams of CaCO₃, and 1 French degree of hardness means 10 grams per cubic metre. 60 ÷ 10 = 6 m³·°Fr, meaning every litre of resin can soften 6 cubic metres of water at 1 °Fr.
| Hardness | How it shows itself | Resin needed |
|---|---|---|
| 15 °Fr | Soft — limescale complaints are rare | 6 litres |
| 25 °Fr | Moderately hard — marks start in the kettle | 10 litres |
| 35 °Fr | Hard — visible limescale in white goods | 14 litres |
| 45 °Fr | Very hard — elements and fittings have a shorter life | 18 litres |
| 55 °Fr | Extremely hard — softening is essential | 22 litres |
| Household | Daily consumption | 4 daily volume | Resin needed |
|---|---|---|---|
| 2 person | 0.3 m³ | 1.2 m³ | 7 litres |
| 4 person | 0.6 m³ | 2.4 m³ | 14 litres |
| 6 person | 0.9 m³ | 3.6 m³ | 21 litres |
| 8 person | 1.2 m³ | 4.8 m³ | 28 litres |
The second limit: instantaneous flow
The resin volume tells you how much water can be softened between regenerations; it does not tell you how many taps the unit can supply at once. The second limit is instantaneous flow, and it has to do with the diameter of the plumbing itself. In a flat, a shower and a washing machine may run at the same time; in a hotel, dozens of points. That is why a twin-tank build is preferred at scale rather than a single vessel — while one regenerates the other stays in service and the water is never cut.
Table 6
The same water problem is met by a different solution at a different scale. Every row below is tied to a real category in the catalogue.
| Place of use | Typical scale | Solution group |
|---|---|---|
| Flat | 150 – 600 L/day | Domestic / Office Water Purifier Water Softening System |
| Detached house and villa | 600 – 1,500 L/day | Flat and Building Inlet System Water Softening System |
| Apartment block and estate inlet | 5 – 20 m³/day | Flat and Building Inlet System Water Softening System |
| Café, restaurant, office | 1 – 5 m³/day | Water Dispenser with Treatment Reverse Osmosis System |
| Production plant | According to the flow profile | Industrial Water Treatment System |
| Laboratory and process | According to the conductivity target | Pure Water / Deionised System |
| Anywhere on well water | Cannot be set without an analysis | Well Water Treatment System |
Frequently asked
The questions here were not invented: they were chosen from the queries that were genuinely searched on this site in the Search Console records and that the site could not answer.
The usable volume of an 8 litre tank is about 5 litres; the rest is taken up by the air cushion. A 50 GPD system without a pump fills that volume in 1 hr – 1 hr 30 min, a pumped 300 GPD system in 8 min – 9 min. The time lengthens as mains pressure falls, as the water gets colder and as the membrane ages.
The difference is where the pressure driving the membrane comes from. A unit without a pump works on mains pressure alone, and its output falls quickly below 3 bar. A pumped unit produces the pressure itself; even on a line as low as 1.5 bar it delivers the output on its label. The practical result shows in the tank fill time: the same 8 litre tank takes between half an hour and 1.5 hours on a system without a pump, and 6–9 minutes on a pumped one. In return, a pumped unit needs electricity and is audible while it runs.
The resin volume is found with this formula: daily water consumption (m³) × hardness (°Fr) × days between regenerations ÷ 6. The number in the divisor is the exchange capacity of the resin — 1 litre of standard cationic resin holds about 60 grams of CaCO₃, and 1 French degree of hardness means 10 grams per cubic metre. For example: if a four-person household uses 0.6 m³ of water a day, the water is 35 °Fr and the unit regenerates every four days, the resin needed is 14 litres.
In a four-person flat, daily consumption is taken as roughly 0.6 m³. At 35 °Fr hardness and a four-day regeneration interval, that comes to 14 litres of resin; in the catalogue that corresponds to a cabinet-type softener. If the hardness is 55 °Fr, the resin needed for the same household rises to 22 litres. Household size alone therefore does not set the capacity; share your hardness value and we will work out the capacity that suits you best together.
GPD means "US gallons per day", and one US gallon is 3.785 litres. 300 GPD therefore means 1,136 litres a day, or roughly 47 litres an hour. By the same calculation, 50 GPD is 189 litres a day, 500 GPD is 1,893 litres a day and 1,000 GPD is 3,785 litres a day.
Up to two people, an 8 litre tank is enough. Between three and six people, a 12 litre tank is preferred. At seven people and over the logic of a tank breaks down — you have to wait each time it empties; at that scale the right answer is a direct-flow system with no tank. What decides the tank volume is not the daily output of the unit but the water standing ready when the tap is opened.
No. A system chosen larger than necessary costs more and works inefficiently, because it runs below its design flow. In softening, a large resin bed will not regenerate for days on low consumption, and stagnant water is left in the bed. In reverse osmosis, an oversized membrane produces more reject water at low draw. The right choice is the smallest system that meets the need; the assistant ranks products by that same rule.
WaterAI is a system selection tool that works on the technical data of the Water Point catalogue. Six questions capture where you will use it, your water source and your consumption; it converts the capacity values in the catalogue — written in different units such as "5 Tonnes/Day", "300 GPD" and "8 m³/Hour" — onto a single axis and puts the smallest system that meets your need first. It is a rule engine, and the result screen states plainly which assumptions it worked from. If you share your water analysis values, we will build the system around them.
How it works
Home, villa, building inlet, business, factory or laboratory — each corresponds to a different solution family and a different scale.
The treatment build for mains water and for well water is completely different. Limescale, sediment, conductivity and microbiological risk each call for separate stages.
From the number of people, or from the daily consumption you state, it derives a need in litres per day. The assumptions it uses are the same as the tables above, and they are written out on the result screen too.
The capacity values in the products' technical tables — "5 Tonnes/Day", "300 GPD", "8 m³/Hour" — are converted onto a single axis, and the smallest system that meets your need is put first.
The tables here give you the scale of your need. Share the hardness, iron, pH and conductivity values of your water and we will prepare the system that best suits what you want — on well water in particular, we build the stages around these values. If you do not know the values, we will tell you which measurements to have taken.
The site survey is free when the system is purchased from us. A survey fee of ₺2,000 applies if you request the survey and measurement only.
Further reading
This page gives you the calculation. The articles below explain in detail why the calculation works as it does, what the stages are for and what the selection criteria are.
Water Treatment Technologies
The tables above give you the scale of your need. Request a site visit or send us the water analysis report you have; we will size and prepare the system that best suits what you want, against the figures.