Buying "whatever tank size Shopee recommends" instead of sizing for your household? Get your water system designed right.
Most homeowners size their water tank by whatever number shows up first on an online shop — usually a flat 500L or 1,000L poly tank, regardless of household size. That works for some households and badly undersizes others. The National Plumbing Code sets a floor for this (minimum 1-day storage where supply is intermittent), but the number that actually matters is your real daily demand: how many people, how much each one uses, and how many days of buffer you want. Here's how to work that out, plus a calculator that does it for you.
The National Plumbing Code's water supply provisions (Chapter 6 — Water Supply) address storage directly for one specific situation: where the utility water supply is intermittent, an approved storage tank providing a minimum of one day's supply must be installed. That's a floor, not a target — it tells you the minimum buffer required when your connection isn't 24/7 reliable, not the ideal size for your household. Most engineers size tanks well above this minimum for comfort, especially in areas with known scheduled interruptions or low water pressure hours.
Chapter 6 also covers Water Supply Fixture Units (WSFU), distribution pipe sizing, cross-connection control, and backflow prevention — see the full chapter reference.
Open the Full Chapter 6 ReferenceThe Plumbing Code's 1-day rule doesn't tell you how big "1 day" actually is in liters — that depends on real per-capita demand. LWUA's (Local Water Utilities Administration) standard reference figure is about 140 liters per person per day for a household of 6. Actual usage varies a lot by income and location: studies in Metro Manila have found a range from roughly 90 LPCD in lower-income households up to 260+ LPCD in higher-income households, driven mainly by personal hygiene, laundry, and sanitary use. 150 liters per person per day is a reasonable, slightly conservative planning default for most Philippine residential design — it's what the calculator below uses unless you change it.
Enter your household size and storage buffer to get a required total volume, split into cistern and overhead tank.
Splitting storage between a ground-level cistern and a rooftop/elevated overhead tank is common Philippine practice, not a Plumbing Code requirement. The cistern holds the bulk of the reserve and is fed by the utility connection, a deep well, or both; a pump lifts water to the overhead tank, which then feeds fixtures by gravity or a small pressure booster. A frequently used rule of thumb is roughly one-third of total storage in the overhead tank, two-thirds in the cistern — enough elevation head for reasonable fixture pressure without an oversized (and structurally heavier) roof tank. Some setups skip the overhead tank entirely and use a pressure pump drawing straight from the cistern; that trades tank elevation for pump reliability and backup power during outages.
Buying one flat tank size for every household. A 500L or 1,000L poly tank is what most hardware stores stock as a default, regardless of whether it's serving a 2-person condo unit or a 10-person household. Sizing against your actual occupant count and demand — not the store's default SKU — is the difference between a comfortable buffer and running dry mid-outage.
Locally available tanks are usually sold in these increments: 500L, 750L, 1,000L, 1,500L, 2,000L, 3,000L, 5,000L, and 10,000L (concrete or fiberglass cisterns can be custom-poured beyond that for larger buildings). Always round up to the next available size, not down — a tank sized exactly to your calculated demand leaves zero buffer for an unusually heavy usage day, a delayed refill, or a longer-than-expected supply interruption.
AEDO's engineers size cisterns, overhead tanks, pumps, and distribution piping against real demand and NPC Chapter 6 — with sealed plans your LGU will accept.
AEDO Construction provides full design services (sanitary/plumbing, structural, electrical, architectural) anywhere in the Philippines, plus full design-build execution in Negros Oriental.
"Just get the 1,000L tank everyone buys" isn't sizing — it's a guess that happens to work for some households and fails others. Multiplying real occupant count by per-capita demand and your desired buffer days tells you exactly what cistern and overhead tank size your household actually needs.
A common starting point is occupants × 150-200 liters per person per day × number of storage days you want as a buffer. A 5-person household at 150 LPCD with 1 day of storage needs about 750 liters minimum; many homeowners size for 1.5-2 days (1,100-1,500 liters) for comfort during brief interruptions.
Yes. NPC Chapter 6 (Water Supply) requires that where the utility water supply is intermittent, an approved storage tank providing a minimum of one day's supply must be installed. This is a floor, not a target — many engineers size for more than 1 day where supply reliability is a known issue.
LWUA's standard reference figure is about 140 liters per person per day for a household of 6. Actual consumption varies widely — from roughly 90 LPCD for lower-income households up to 260+ LPCD for higher-income households in studies of Metro Manila. 150 LPCD is a reasonable planning default.
It's common practice, not a code requirement: a ground-level cistern holds the bulk reserve and a smaller elevated tank feeds fixtures by gravity, refilled from the cistern. A frequent rule of thumb is roughly one-third overhead, two-thirds cistern, though this varies by pump setup and building height.