Comparing Emergency Go-Bags and Home Stockpiles in Japan: How to Calculate Water, Food, and Toilet Needs

The most common mistake when preparing for disasters in Japan is either putting all water and food into an emergency backpack or, conversely, stockpiling everything only at home. A disaster preparedness backpack contains emergency items for immediate evacuation, while home supplies are resources for enduring water outages, power outages, and supply disruptions when the home is safe.

The two types of preparation do not replace each other. For most households, the best approach is to have both a lightweight backpack for each person and sufficient supplies at home.

Differences Between a Disaster Preparedness Backpack and Home Supplies

The key is not to pack several days’ worth of everything into a backpack, but to keep the items essential during evacuation within a weight that can actually be carried. Putting the water and food that should remain at home into the backpack can slow evacuation and increase the risk of falling.

Calculating Quantities of Water, Food, and Portable Toilets

Water for Home Use

Public disaster preparedness guidance in Japan generally calculates household water as follows.

Number of household members × about 3 liters per day × number of stockpiled days

This is mainly the amount needed for drinking and simple cooking. Water needed for washing, cleaning, pets, cleaning medical equipment, and other daily uses must be considered separately.

Because stored water is heavy, calculate the amount after checking the official recommendation from your local municipality; carrying several days’ worth of drinking water in a backpack is not realistic. Putting this amount into a backpack is not realistic. Dividing water among several containers rather than relying on one large container makes storage, transport, and the risk of container damage easier to manage.

Water in a Disaster Preparedness Backpack

There is no single nationwide correct amount of water to put in a backpack. It varies according to travel distance, weather, physical strength, shelter location, and whether infants will be accompanying you.

Use the following principles to decide.

• Put on the fully packed backpack and walk up and down stairs and along the actual evacuation route.
• You should be able to use both hands freely with the water packed.
• Divide the water among family members who can walk, taking differences in physical strength into account.
• Include a collapsible water container or empty container for refilling, but it does not need to be filled from the start.
• Water purification products differ in their ability to remove different types of contaminants, so do not assume they can replace a safe water source.

Food

The basic quantity of home food supplies can be calculated as number of household members × number of meals per day × number of stockpiled days. However, do not focus only on the number of meals; include foods that can be eaten without water or a heat source.

• Ready-to-eat foods: canned foods, nutrition bars, instant porridge, etc.
• Foods requiring water or a heat source: dried noodles, packaged instant rice, freeze-dried foods, etc.
• Foods regularly eaten and replenished: rice, noodles, retort-pouch foods, and side dishes with a long shelf life
• Foods for individual needs: allergy-friendly foods, low-sodium foods, easy-to-chew foods, and food for infants and young children

If you include canned food, check whether it can be opened by hand and store a can opener and utensils with it if necessary. Rather than buying emergency food and storing it separately, a rolling-stock system—using stored foods that you normally eat first and replenishing them with new products—is more effective for managing expiration dates.

Portable Toilets

When damage to sewer pipes is suspected, as well as during a water outage, pouring water into a toilet to flush it can worsen the problem. It is therefore safer to separately stock portable toilets that use solidifying agents and bags.

Use the following formula.

Number of household members × expected number of uses per person per day × number of stockpiled days

Set the expected number of daily uses according to your family’s circumstances, and confirm the quantity needed using guidance or an official calculation tool from your local municipality. This is an example for planning purposes, and the actual number may vary depending on pregnancy, health conditions, medications, and age. Toilet supplies require not only solidifying agents but also toilet bags, sealable disposal bags, gloves, disinfectant, and odor-control measures.

Is It Better to Assemble Your Own Kit or Buy a Ready-Made Disaster Preparedness Kit?

Although a ready-made kit may look complete, it is actually closer to a starting point. Before buying one, check the weight of the bag itself, the quantities of water and food, the radio’s power source, the flashlight battery specifications, the number of portable toilet uses, and food expiration dates.

A low-cost kit may look advantageous when comparing price alone, but you should also consider the total cost after adding the required quantities and the actual carrying weight. It may be better to put only the necessary items into an existing backpack than to buy a kit containing many tools your family does not need.

Items to Add According to Family Composition

If You Have Infants or Young Children

• The formula, baby food, and allergy-friendly foods they normally consume
• Feeding supplies, bottle-care supplies, and disposable cups
• Diapers, wet wipes, skin-protection products, and disposal bags
• A baby carrier and a blanket for maintaining body temperature
• Contact details for guardians and the child’s medical information

Formula requires safe water and a preparation method appropriate for the product. Ready-to-feed liquid products can reduce the burden of preparation, but first check whether the child can normally consume them and what storage conditions they require.

Family Members Who Are Older Adults or Have Disabilities

• Glasses, hearing aids, and spare batteries
• Dentures and cleaning and storage supplies
• Canes, walking aids, and communication cards
• Adult diapers and skin-care products
• Foods that are easy to chew or swallow
• Alternative means of charging or powering devices normally used

If Someone Takes Medication or Has a Chronic Condition

• Medications and their original packaging or prescription labels
• A list recording medication names, dosages, and times taken
• A copy of Okusuri Techo, Japan’s medication notebook, or offline information from the relevant app
• Contact details for medical institutions and pharmacies
• Medical device consumables and backup power sources

The amount and method for obtaining extra prescription medication vary according to the type of medication and the conditions of medical care. Do not reduce doses at your own discretion or store old medication; ask a doctor or pharmacist how to prepare for disasters.

If You Have Pets

Rules for bringing pets to shelters vary by municipality and facility. Prepare a carrier, food, water, waste-disposal supplies, medication, vaccination records, and photographs, and check how pets are accommodated at the actual designated shelter.

Principles for Dividing Supplies Among Family Members

If shared family supplies are concentrated in one person’s bag, no one will be able to use them if that person becomes separated from the group or the bag is lost.

• Each person should prioritize carrying their own water, medications, light, contact details, and items for staying warm.
• Adults should divide shared items such as radios, tools, and chargers among themselves.
• Distribute supplies for infants and young children between two guardians.
• Decide the weight of children’s and older adults’ bags based on their actual walking ability rather than applying a uniform weight standard.
• Weigh the completed bags and test them on stairs and along the evacuation route while wearing shoes.
• If flooding is possible, place important documents and electronic devices in waterproof pouches.

Avoid writing sensitive personal information prominently on the outside of a bag. You may instead record the necessary information on a sealed contact card inside.

Why You Must First Decide the Type of Disaster and Evacuation Method

Before making an item list, determine under what circumstances you will leave your home. Even for the same home, the best choice varies by type of disaster.

This is an area that simple checklists often overlook. First use the Ministry of Land, Infrastructure, Transport and Tourism’s Hazard Map Portal and maps from your local municipality to check flood, tsunami, and landslide risks and the locations of designated shelters. If the municipality advises evacuation or the building is unsafe, do not remain at home merely to protect your supplies.

How to Check Supplies at Evacuation Shelters

Do not skip personal preparations simply because a shelter has water and food. Stored quantities, items, and opening conditions vary by facility, and distribution may be delayed by road damage or power outages.

Check the following items.

1. On your local municipality’s website, distinguish between designated evacuation shelters and designated emergency evacuation sites.
2. Look for each shelter’s stockpile warehouse inventory, regional disaster management plan, and shelter operation manual.
3. Check whether water, food, blankets, portable toilets, generators, and mobile phone charging options are available.
4. Check whether individuals must prepare food for infants and young children, allergy-friendly food, menstrual products, and medications.
5. Check the rules for bringing pets, support for people with disabilities, and conditions for using welfare shelters.
6. If the published information is outdated or does not provide quantities by facility, contact the municipality’s disaster management department.

Published quantities are not portions allocated to specific individuals. It is also advisable to separately check evacuation facilities near workplaces or schools where family members spend the daytime.

Managing Expiration Dates and Storage Locations

Maintaining supplies so they remain usable is harder than purchasing them. Record the following items in a table or mobile phone document.

In practical terms, management is easier if supplies are inspected once every six months, before typhoon and heavy-rain seasons, and after moving or changes in family composition. The six-month interval is not a statutory standard but an operational method for reducing omissions.

• Place foods with shorter expiration dates at the front and consume them first in daily life.
• If you do not buy all food on the same day, replacement times will be spread out.
• Follow the manufacturer’s stated storage conditions and dates for bottled water.
• Check batteries left inside devices for leakage.
• Replace clothing, rain gear, and shoes with seasonally appropriate sizes and account for growth.
• Update medications and medical information whenever prescriptions change.
• Check that furniture or falling objects will not block access to the backpacks.

How to Cross-Check Quantities Using an Official Calculation Tool

The Tokyo Metropolitan Government’s 東京備蓄ナビ is an official tool that lets users enter household composition and housing conditions to check stockpile items and quantities. Because the results are reference figures based on living conditions in Tokyo, they must be adjusted according to guidance from your local municipality, individual medical conditions, and evacuation routes.

Rather than using the calculation results directly as a shopping list, review them in the following order.

• Exclude food and household supplies already at home.
• Check the proportion of foods requiring cooking water or a heat source.
• Supplement portable toilets, hygiene supplies, and items for infants, young children, and older adults.
• Decide on storage space, then acquire supplies gradually rather than buying everything at once.
• Separately set aside items to be transferred to disaster preparedness backpacks and test their actual weight.

Final Selection Criteria

For most households, a distributed combination of disaster preparedness backpacks and home supplies is appropriate. However, the following questions can help determine where to allocate more budget and space.

• Is the home in an area at risk of flooding, tsunamis, or landslides?
• If a warning is issued, how quickly must you evacuate on foot?
• When the home is safe, is there space to remain there for at least 3 days and up to 1 week?
• Can water be moved without an elevator?
• Does the family include infants, young children, older adults, people with disabilities, or people who take medication?
• What personal essentials are not stocked at designated shelters?

If rapid evacuation is the priority, backpacks should be lighter and more personalized. If sheltering at home is more likely, strengthen home supplies in the order of water, portable toilets, food, and power sources. In either case, a backpack that cannot actually be carried and expired supplies can hardly be considered prepared resources.