School Drinking Water: Sizing by Students and Breaks

Take 15 L per student and 90% attendance. Daily demand is 800 × 15 × 0.9 ÷ 1,000 = 10.8 m³/day. Size the RO on refill hours, not on the break: 10.8 × 1.15 ÷ 8 = 1.55 m³/h, so a 2 m³/h unit is the next standard size. A 2–3 m³ tank gives about 20–28% of daily demand and covers the morning break without draining the reserve.

Now check the break separately. If 800 students each drink 0.2 L in a 10-minute break, the demand is 160 L in 10 minutes, or 0.96 m³/h. That is below the 2 m³/h RO, but only if storage is full at the start of the break. The tank, not the membrane, serves the break; the membrane refills the tank afterwards. This is why schools fail when storage is sized from the daily average alone.

A school compresses drinking into two or three windows. In a 10-minute break, a student may have 3–5 minutes of actual drinking time after walking to the fountain and queuing. At 0.2 L per student, 800 students need 160 L delivered in that window. Ten outlets flowing at 1.5 L/min deliver 15 L/min, or 150 L in 10 minutes — just enough, with no reserve for the next break if the tank has not refilled.

Longer breaks reduce the instantaneous rate but not the total. A 20-minute break halves the required flow to about 0.48 m³/h, while a 5-minute break doubles it. The fountain count should be checked against the walking distance between classrooms and the nearest outlet; a school with distant fountains needs more storage or more outlets, not a larger membrane.

Start from storage, not from the membrane. Set tank volume to cover one full break plus 20–30% of daily demand, then size the RO to refill that tank within 6–10 hours. For the 800-student example, a 2–3 m³ tank and a 2 m³/h RO refill a full tank in about one hour, leaving ample time between breaks. Fountains are sized on outlets and pressure, not on RO flow.

Keep the drinking loop separate from the canteen and toilet supply. The loop should return to the tank through UV, with 1–2 bar at the farthest fountain and a 5 µm cartridge before the UV. If the building has several floors, use a small booster set and balance valves; a single riser feeding 20 outlets will starve the top floor during the break.

Drinking water at a school should be clear, tasteless and microbiologically safe. Turbidity below 1 NTU and no visible colour are the first checks; chlorine should be removed at the point of use because it suppresses consumption, but disinfection must continue downstream. UV at 30–40 mJ/cm² after storage is the usual barrier, with a 5 µm cartridge ahead of the lamp to keep the sleeve clean.

Test the raw water for iron, manganese, nitrate and hardness before choosing the train. Iron above 0.3 ppm stains fountains and fouls cartridges; nitrate above the local limit requires RO; hardness above 120 ppm scales the canteen dishwasher and combi oven. If the school draws from a borehole, add a sediment filter and a chlorine or UV barrier, and test microbiology at least twice a year.

Boarding schools add showers, laundry and evening demand, so the plant is a building-scale system rather than a drinking-water skid. Plan 40–80 L per student per day for the whole building, keep the drinking loop separate, and size the softener on the laundry and hot water load. Canteens need their own softener and a grease trap ahead of any drain connection.

Hot climates raise drinking consumption by 15–25% and push students to drink more frequently between lessons. Add fountains in shaded corridors, chill the water to 10–15 °C if the budget allows, and check that the UV lamp is not overheated in an unventilated plant room. In cold climates, protect the loop from freezing and confirm that the RO feed is above 5 °C.

A school plant sits idle for long holidays, which is when tanks and dead legs become a microbiological risk. Maintenance should follow the calendar: a full flush and shock disinfection before term starts, filter and UV replacement during the break, and a documented weekly check while school is in session.