Purifying Water During an Emergency

This document was produced in cooperation with the Emergency Management Division of the Washington State Military Department.


The treatments described below work only in situations where the water is unsafe because of the presence of bacteria or viruses. If you suspect the water is unsafe because of chemicals, oils, poisonous substances, sewage or other contaminants, do not use the water for drinking.

Storing water safely

• Store one gallon of water per person per day.
• Store at least a three-day supply of water per person.
• Collect the water from a safe supply.
• Thoroughly washed plastic containers such as soft drink bottles are best. You can also purchase food-grade plastic buckets or drums.
• Seal water containers tightly, label with date, and store in a cool, dark place.
• Replace water every six months.
• Never reuse a container that contained toxic materials such as pesticides, solvents, chemicals, oil or antifreeze.

Water purification

There are two primary ways to treat water: boiling and adding bleach. If tap water is unsafe because of water contamination (from floods, streams or lakes), boiling is the best method.

• Cloudy water should be filtered before boiling or adding bleach.
• Filter water using coffee filters, paper towels, cheese cloth or a cotton plug in a funnel.

Boiling

• Boiling is the safest way to purify water.
• Bring the water to a rolling boil for one minute.
• Let the water cool before drinking.

Purifying by adding liquid chlorine bleach

• If boiling is not possible, treat water by adding liquid household bleach, such as Clorox or Purex. Household bleach is typically between 5 percent and 6 percent chlorine. Avoid using bleaches that contain perfumes, dyes and other additives. Be sure to read the label.
• Place the water (filtered, if necessary) in a clean container. Add the amount of bleach according to the table below.
• Mix thoroughly and allow to stand for at least 30 minutes before using (60 minutes if the water is cloudy or very cold).

 

Treating Water with a 5-6 Percent Liquid Chlorine Bleach Solution
Volume of Water to be Treated	Treating Clear/Cloudy Water: Bleach Solution to Add	Treating Cloudy, Very Cold, or Surface Water: Bleach Solution to Add
1 quart/1 liter	3 drops	5 drops
1/2 gallon/2 quarts/2 liters	5 drops	10 drops
1 gallon	1/8 teaspoon	1/4 teaspoon
5 gallons	1/2 teaspoon	1 teaspoon
10 gallons	1 teaspoon	2 teaspoons

DOH Pub 821-031
Revised - January 2009

Rating Battery Output and Storage Capacity

Battery Application & Technology

In general terms, the capacity of a cell/battery is the amount of charge available expressed in ampere-hours (Ah). An ampere is the unit of measurement used for electrical current and is defined as a coulomb of charge passing through an electrical conductor in one second. The capacity of a cell or battery is related to the quantity of active materials in it, and the amount of electrolyte and the surface area of the plates. The capacity of a battery/cell is measured by discharging at a constant current until it reaches its terminal voltage (usually about 1.75 volts). This is usually done at a constant temperature, under standard conditions of 25C  (77F). The capacity is calculated by multiplying the discharge current value by the time required to reach terminal voltage.

The most common term used to describe a battery's ability to deliver current is its rated capacity. Manufacturers frequently specify the rated capacity of their batteries in ampere-hours at a specific discharge rate. For example, this means that a lead-acid battery rated for 200 Ah (for a 10-hour rate) will deliver 20 amperes of current for 10 hours under standard temperature conditions (25C or 77F). Alternatively, a discharge rate may be specified by its charge rate or C-rate, which is expressed as a multiple of the rated capacity of the cell or battery. For example, a battery may have a rating of 200 Ah at a C/10 discharge rate. The discharge rate is determined by the equation below:

Battery capacity varies with the discharge rate. The higher the discharge rate, the lower the cell capacity. Lower discharge rates result in higher capacity. Manufacturer's literature on batteries will normally specify several discharge rates (in amperes) along with the associated discharge time (in hours). The capacity of the battery for each of these various discharge rates can be calculated as discussed above.

The rated capacity for lead-acid batteries is usually specified at the 8-, 10-, or 20-hour rates (C/8, C/10, C/20). UPS batteries are rated at 8-hour capacities and telecommunications batteries are rated at 10-hour capacities.