How to Size a Commercial RO Plant for a Restaurant or Hotel

Choosing between a 250, 500, or 1,000 LPH commercial RO plant is not simply a question of seating capacity or number of hotel rooms.

The correct capacity depends on how much RO-quality water each application needs, when that demand occurs, how many hours the plant can operate, how much usable storage is available, and how the selected membrane performs with the site's actual feed-water quality, temperature, pressure, and recovery.

This guide explains the commercial RO sizing process for Indian restaurants and hotels, including the formulas, information required, common mistakes, and a worked example.

First decide whether RO is required

RO is a membrane-separation process. Feed water is pressurised against a semi-permeable membrane, producing:

• permeate or product water, which passes through the membrane; and
• concentrate or reject water, which retains a higher concentration of many rejected constituents.

The US Environmental Protection Agency describes RO as useful for reducing many inorganic constituents and dissolved solids, but also notes that the process creates a concentrate stream, consumes energy, and frequently requires pretreatment to reduce fouling or plugging. [Source: US EPA overview of RO and nanofiltration]

RO should therefore be selected because a verified source-water or application requirement justifies it—not because “commercial kitchen” automatically means “RO.” Depending on the report and end use, a project may require sediment filtration, activated carbon, softening, UV, RO, or a combination.

Questions to answer before sizing include:

• Which measured parameters must be reduced?
• What treated-water specification is required?
• Which applications genuinely require RO permeate?
• Could softening, filtration, carbon, disinfection, blending, or a different source meet another part of the requirement more appropriately?
• What will happen to the concentrate stream?

Overall building demand is not RO-product demand

Indian building-water norms can help estimate total site requirements, but they should not be applied blindly to RO production.

IS 1172:1993 lists 70 litres per seat per day for restaurants and 180 litres per head per day for hotels in its table of water requirements for buildings other than residences. More recent building-bye-law material based on NBC 2016 separates domestic and flushing demand and distinguishes hotel categories. [Sources: Ministry of Housing and Urban Affairs copy of IS 1172] and [Model Building Bye-Laws table referencing NBC 2016]

These figures are overall planning references. They can include uses that normally do not require RO permeate, such as flushing and some cleaning or utility applications. A hotel's room count also does not capture laundry, kitchen, staff, banquet, pool, cooling, landscaping, or water-body demand where those are outside a cited norm.

Use the applicable building code and local authority requirement for total water infrastructure. Size the RO plant separately from the verified RO-quality water demand.

The six quantities needed for RO sizing

Commercial RO sizing requires six linked quantities:

1. Daily permeate demand: litres of RO product required per day.
2. Peak permeate demand: litres required during the busiest service window.
3. Effective operating hours: hours in which the plant can actually produce water.
4. Usable treated-water storage: water available between the operating high and low levels of the tank.
5. Design recovery: the fraction of feed converted to permeate under the projected operating condition.
6. Feed-water and product-water specifications: the chemistry and performance basis used for membrane projection and pretreatment design.

Ignoring any one of these can produce an undersized plant, excessive storage, unnecessary capital cost, unstable operation, or an unmanageable reject stream.

Step 1: Create an application-wise demand schedule

List every possible RO user, then confirm whether it needs RO-quality water.

Restaurant demand worksheet

Do not assume that the full kitchen water supply should pass through RO. Some equipment may require softened, filtered, or application-conditioned water rather than very low-TDS water.

Hotel demand worksheet

Separate hotel demand into circuits:

• guest drinking-water points and refill stations;
• rooms, minibar, and room service;
• restaurants, cafés, bars, banquets, and kitchens;
• ice production on guest and service floors;
• coffee, beverage, and steam equipment;
• staff cafeterias and offices;
• laundry, boilers, cooling, pools, spa, and other utilities; and
• landscaping and flushing.

Only include a circuit in the RO permeate total after defining its required water quality. A centralised hotel RO plant serving selected potable and foodservice applications is a different design from a plant intended for boiler makeup or a broader building supply.

Step 2: Calculate daily RO-product demand

For each approved RO application:

Then add the applications:

Use measured consumption where available. For a new property, use equipment schedules, menu and occupancy assumptions, operating data from comparable sites, and the applicable project specification. Record every assumption so it can be updated before procurement.

Do not add a generic “safety factor” without explaining what uncertainty it covers. Future expansion, seasonal occupancy, banquet peaks, measurement uncertainty, and planned additional equipment should be documented separately. Excessive oversizing can create short cycling, poor storage turnover, and unnecessary cost.

Step 3: Determine realistic production hours

An RO plant does not necessarily produce for 24 hours every day.

Subtract time required for:

• unavailable source-water supply;
• low raw-water tank level;
• pretreatment backwash or softener regeneration where these interrupt RO feed;
• flushing, sanitation, maintenance, or membrane cleaning;
• electrical outages or operating restrictions; and
• high treated-water tank level, when automatic control stops production.

The first-pass production-rate calculation is:

This result is not yet the selected plant capacity. It must still pass the peak-demand, storage, feed-water, recovery, and membrane-projection checks.

Step 4: Check the busiest service window

A plant can meet daily demand and still run out during breakfast, dinner, banquet setup, or simultaneous ice and kitchen production.

For a selected service window:

If the result is positive, the usable treated-water tank must cover at least that deficit plus the project's separately defined operational reserve.

Storage is not a substitute for adequate production, and production is not a substitute for storage. The design must balance plant size, usable tank volume, refill time, available space, hygiene, and the consequence of downtime.

When checking a tank, distinguish:

• nominal tank capacity;
• usable capacity between control levels;
• minimum pump suction level or dead volume;
• reserve held for a defined contingency; and
• water turnover under normal demand.

Step 5: Calculate feed and concentrate flow from recovery

RO recovery is the percentage of feed flow converted to permeate:

Rearranging:

These material-balance relationships are standard RO definitions. [Source: US EPA technical documentation defining recovery]

Do not choose recovery merely to advertise low reject. The US EPA notes that raising recovery increases dissolved-solids concentration in the reject and can increase feed-pressure and membrane-scaling risk. Achievable recovery depends on source-water quality and pretreatment. [Source: US EPA RO/NF cost and design model]

The project recovery should come from a membrane-system projection using complete feed chemistry, membrane arrangement, antiscalant or other pretreatment assumptions, and manufacturer limits.

Step 6: Build the membrane projection from a complete feed analysis

A basic drinking-water report may not contain everything needed for RO design.

The membrane designer may need:

• pH and temperature range;
• conductivity or TDS with ionic analysis;
• calcium, magnesium, sodium and potassium;
• alkalinity, bicarbonate and carbonate;
• chloride, sulphate, nitrate and fluoride;
• silica;
• iron, manganese, aluminium and barium/strontium where relevant;
• turbidity and Silt Density Index (SDI);
• total organic carbon or other organic indicators where relevant;
• free chlorine or other oxidants;
• microbiological or biofouling risk; and
• source variability and chemical dosing upstream.

DuPont's FilmTec feed-water guidance states that the temperature should be provided as a range and notes that temperature variation can affect scaling potential, particularly where silica and bicarbonate are high. It also recommends periodic feed-water analysis after commissioning so pretreatment and operation can be adjusted. [Source: DuPont FilmTec Feedwater Type and Analysis]

Use the membrane manufacturer's current design software or validated projection method. DuPont's WAVE platform, for example, models RO/NF, ultrafiltration, and ion exchange as linked treatment processes. [Source: DuPont WAVE PRO]

The projection should document at least:

• membrane model and quantity;
• array or staging;
• feed-water composition and temperature;
• feed pressure;
• permeate flow and quality;
• recovery and concentrate flow;
• element flux and recovery limits;
• concentration and scaling indices;
• chemical-dosing assumptions; and
• predicted performance at relevant minimum, normal, and maximum conditions.

Why nameplate LPH is not enough

A membrane element's published flow is measured under specified standard test conditions. It is not a promise of identical output at every site.

For example, DuPont lists standard test conditions for one class of brackish-water RO membrane at 2,000 ppm NaCl, 225 psi, 25°C, pH 8, and 15% element recovery. Actual system output depends on net driving pressure, feed salinity, temperature, membrane condition, recovery, and system arrangement. [Source: DuPont brackish-water RO product conditions]

DuPont's technical manual explains that permeate flow declines as salinity and osmotic pressure increase through a membrane train. It also notes that permeate flux falls when feed-water temperature decreases, which is a normal temperature effect rather than, by itself, proof of fouling. [Source: DuPont FilmTec RO/NF Technical Manual]

For Indian sites, use the actual expected feed-temperature range. Do not select capacity only from a catalogue value at 25°C, and do not assume that a hot summer reading represents winter or monsoon performance.

Pretreatment affects sustainable output

An RO plant sized without pretreatment design may deliver the required flow initially and then lose performance through fouling, scaling, oxidation, or pressure loss.

DuPont's FilmTec feed-water guideline lists membrane-entry recommendations including SDI not above 5 and turbidity not above 1 NTU for the cited membrane family. It also provides limits and conditions for oxidants, iron, manganese, aluminium, organics, and other constituents. These are manufacturer guidelines, not universal values for every membrane. [Source: DuPont FilmTec Guidelines for Feedwater Quality]

Depending on the source, pretreatment may include:

• raw-water storage and controlled pumping;
• media or cartridge filtration;
• activated carbon or another dechlorination process;
• softening or antiscalant dosing;
• iron and manganese treatment;
• pH adjustment;
• ultrafiltration; and
• final guard filtration.

Each stage must be justified by the feed analysis, membrane requirements, peak flow, and operating plan.

Worked restaurant sizing example

The following is a fictional calculation that demonstrates the method. It is not a universal recommendation or a DhwaNeer project result.

Assumed application demand

Assume the plant has 6 effective production hours per day after accounting for source availability and operational stops.

This establishes a first-pass production rate of 250 LPH.

Peak-window check

Assume the restaurant needs 900 L during a three-hour combined preparation and service window, and the plant can operate throughout that period.

If the project separately defines a 250 L operational reserve, the required usable treated-water storage for this simplified check becomes:

The nominal tank selected would have to account for control levels, dead volume, pump suction, and sanitary design. A nominal 400 L tank does not necessarily provide 400 L of usable storage.

Feed and concentrate check

Assume a membrane projection—not a rule of thumb—supports 65% system recovery at the design condition.

At 1,500 L/day permeate output:

These values show why source availability, drain capacity, and concentrate management must be checked during sizing. The assumed 65% recovery is used only to demonstrate the equations; the real value must come from the complete water analysis and membrane projection.

Does this mean a 250 LPH plant should be purchased?

Not yet. Before selection, verify:

• demand assumptions and future equipment;
• winter/lowest-temperature projected output;
• feed-water chemistry and source variation;
• membrane model and sustainable projection;
• pretreatment downtime;
• peak storage and refill time;
• redundancy and acceptable outage;
• product-water quality at beginning and end of membrane life;
• pump, tank, drain, power, and space availability; and
• local requirements for concentrate discharge or approved reuse.

The final selected capacity may differ after these checks.

Hotel RO sizing needs diversity and redundancy checks

Hotels create additional sizing challenges because demand is distributed across rooms, restaurants, banquets, staff areas, ice machines, and utilities.

Check:

• occupied rooms, not only total rooms;
• normal, weekend, seasonal, and event occupancy;
• banquet demand that can coincide with restaurant peaks;
• simultaneous ice production on several floors;
• whether laundry, boiler, cooling or spa water is on a separate treatment train;
• treated-water distribution pressure and elevation;
• reserve needed during membrane service; and
• whether one large train or multiple duty/standby trains better matches operational risk.

For a critical hotel operation, redundancy should be defined as a service requirement. “Two pumps” or “two membranes” does not automatically mean the plant can deliver the required output during a failure. State the capacity available with the largest planned component or train out of service.

Product-water quality must be specified before capacity

An RO plant is not correctly sized if it produces enough litres but fails the intended quality.

Define the acceptance parameters for each circuit, which may include:

• TDS or conductivity;
• hardness;
• alkalinity;
• chloride or silica;
• pH after post-treatment;
• microbiological quality;
• disinfectant residual where applicable; and
• equipment-manufacturer limits.

For water used as a food ingredient or in contact with food or food-contact surfaces, FSSAI food-service hygiene material requires potable water meeting IS 10500 and contains testing and record provisions based on the supply arrangement. [Sources: FSSAI hygiene requirements] and [FSSAI Food Service Establishment Hygiene Rating Checklist]

RO permeate can require post-treatment, blending, disinfection, hygienic storage, or distribution controls depending on the application. Passing through an RO membrane is not, by itself, a complete food-safety management plan.

Source and seasonal changes can alter the design basis

Restaurants and hotels may receive municipal, borewell, tanker, or mixed water. The feed composition can change when the source or mixing ratio changes.

The Central Ground Water Board's Annual Ground Water Quality Report 2025 found that monsoon-recharge effects on groundwater quality were heterogeneous across India: some locations improved through dilution while others deteriorated, with aquifer type and local contamination load influencing the result. [Source: CGWB Annual Ground Water Quality Report 2025]

Size and project the RO against the documented operating range, not one convenient sample. If a site switches sources, analyse each source and the realistic mixtures that will reach the plant.

Concentrate is part of the sizing calculation

RO concentrate contains the constituents retained from the feed at a higher concentration. It should not automatically be called “wastewater that can be reused anywhere.”

Before any reuse, verify:

• concentrate chemistry at the projected recovery;
• microbiological and chemical suitability for the intended use;
• potential scaling, staining, salinity, corrosion, soil, plant, fixture, or process impact;
• storage and cross-connection controls; and
• applicable local discharge, plumbing, environmental, and occupational requirements.

A reuse plan can reduce freshwater demand only where the concentrate is suitable and the reuse is safely engineered. Otherwise, provide a compliant discharge route.

Common commercial RO sizing mistakes

1. Sizing from TDS alone. TDS does not state daily demand, peak flow, scaling chemistry, fouling risk, or required product quality.
2. Multiplying seats or rooms by a generic number and treating all of it through RO. Overall building demand and RO demand are different.
3. Dividing by 24 operating hours when the plant cannot run continuously. Use effective production hours.
4. Ignoring the peak service window. Daily production can be adequate while the kitchen or hotel runs out at the busiest time.
5. Equating nominal tank volume with usable storage. Control levels and pump requirements reduce usable volume.
6. Assuming catalogue LPH is guaranteed onsite. Published flow depends on test conditions.
7. Choosing the highest possible recovery. Higher recovery concentrates salts and may increase scaling and pressure requirements.
8. Using a basic potable-water report as a complete membrane analysis. RO design may require a broader ionic and fouling assessment.
9. Ignoring the lowest expected feed temperature. Lower temperature can reduce permeate flux.
10. Leaving concentrate management until installation. Feed and reject flows affect tanks, drains, permissions, and cost.
11. Providing no redundancy for a critical hotel. Define the output required during service or component failure.
12. Commissioning only with a TDS meter. Verify flow, pressure, recovery, quality, and treatment objectives under documented conditions.

Information to send for an accurate RO sizing proposal

Provide:

• city and exact site;
• water source or sources;
• recent complete feed-water analysis;
• source temperature range where available;
• daily and peak demand by application;
• restaurant covers, hotel occupancy, banquet and seasonal pattern;
• kitchen, ice, beverage, steam, laundry, boiler and utility equipment schedules;
• manufacturer inlet-water specifications;
• effective hours available for RO production;
• raw- and treated-water tank details;
• available power, pressure, space, drainage and access;
• required product-water specification;
• current water problems and existing treatment; and
• expansion, redundancy and uptime requirement.

Frequently asked questions

Size the system around demand, water and operating reality

Commercial RO sizing is a linked water-quality and demand problem.

The reliable sequence is:

1. verify that RO is required;
2. define which applications need RO permeate;
3. calculate daily and peak demand;
4. establish effective production hours;
5. balance plant output with usable storage;
6. project feed, permeate, recovery and concentrate using complete chemistry;
7. design pretreatment and post-treatment; and
8. verify performance during commissioning.

DhwaNeer designs and executes commercial RO and turnkey water-treatment systems for restaurants, hotels, commercial kitchens, corporate facilities, institutions, and utilities.

Sources and verification notes

This article was fact-checked on 18 July 2026 using primary Indian government, standards, public-health, engineering, and membrane-manufacturer sources.

1. Ministry of Housing and Urban Affairs: IS 1172:1993
2. Model Building Bye-Laws table referencing NBC 2016 occupancy water requirements
3. Bureau of Indian Standards: IS 10500 Drinking Water Specification
4. FSSAI: Hygiene requirements
5. FSSAI: Food Service Establishment Hygiene Rating Checklist
6. Central Ground Water Board: Annual Ground Water Quality Report 2025
7. US EPA: Overview of Drinking Water Treatment Technologies
8. US EPA: RO/NF Work Breakdown Structure-Based Cost and Design Model
9. US EPA: RO verification report defining recovery
10. DuPont FilmTec RO/NF Technical Manual, February 2026
11. DuPont FilmTec Guidelines for Feedwater Quality
12. DuPont FilmTec Feedwater Type and Analysis
13. DuPont WAVE PRO design software
14. DuPont brackish-water RO standard test conditions