Water Storage
Tanks, Cisterns, Aquifers, and Ponds For
Domestic Supply, Fire and Emergency Use

Chapter 1: Thinking About Water
To achieve your design goals for a water system, it is helpful to know what your goals are. The first order of business is to consider:

Why Store Water?
Nearly all water systems include some form of storage, most commonly a tank. Storage can be used to:

• cover peaks in demand
• smooth out variations in supply
• provide water security in case of supply interruptions or disaster
• save your home from fire
• meet legal requirements
• improve water quality
• provide thermal storage and freeze protection
• enable a smaller pipe to serve for a distant source

We're going to consider each of these reasons to store water, then look at design principles to help you frame the goals for your project.

Cover Peaks in Demand
The most common function of water storage is to cover short-term use flows that are greater than the flow of the water source. For example, a tiny, one gallon-per-minute spring supplies 1440 gallons a day. This is several times more than most homes use in a day. However, almost every fixture in the home consumes water at a faster rate than 1 gpm while it is turned on. Even a low-flow shower head uses about 1.5 gpm.

By using water stored in a tank, you can supply water to the shower faster than it is flowing from the spring. On completing the shower, the water will be coming in faster than it is going out, and the tank level will rise back up.

If you had a 10,000 gal tank, you could run a 100 gpm fire hose—creating the kind of blast used to bowl over hostile crowds—on the stored water from this tiny spring, for an hour and a half! Hopefully the fire would be out by then, as the tank would take several days to refill.

Smooth Out Variations in Supply
In some circumstances, your storage needs will be affected by variations in the water supply. For instance, if the supply is rainwater, you will need enough storage to make it through the intervals between rainfalls. A six-month, rainless dry season requires a heck of a lot more storage than the most common kind of variable supply?a well pump that cycles on and off.

If you have a well that taps stored groundwater, a tank will save wear and tear on your pump, because the pump won't have to switch on and off every time you open a tap.

Provide Water Security in Case of Supply Interruptions or Disaster
In many places, the water supply chain from source to tap is long and made of many delicate links. If a cow steps on the supply line, a pump breaks, a wire works loose, the electricity goes out, the city misplaces your check, or there is a natural disaster, your water flow could stop. By locating your storage as few chain links away as possible from your use point, a large measure of security is added.

Appendix D: How to Make Ferrocement Tanks
Ferrocement tanks consist of an armature (framework) of steel reinforcing, which is then covered with a sand-cement plaster. They offer complete flexibility in shape. They have a long life, are cost-competitive when contractor-built, and are owner-buildable in both industrialized and non-industrialized countries.

This section describes how to build ferrocement tanks with various techniques, to a variety of standards and sizes from 250-30,000 gal (1-115 m^3 ). With the aid of an engineer you could adapt the plans up to a 100,000 gal (380 m^3 ) tank. For more on the advantages and characteristics of ferrocement tanks, see Tank Materials/ Ferrocement p. 41.

Heavy-duty Ferrocement Tank Section showing steel armature of rebar and lath, access, inlet, outlet Heavy-duty ferrocement tank (section)

The existing literature on ferrocement tanks is sparse, and each document is narrowly focused: one particular size of one design, or a variety of designs but all for the context of non-industrialized
nations. The heavy-duty ferrocement construction technique described literature before to my knowledge.

This appendix?practically a book in itself?is unique in that it describes the full range of ferrocement techniques in one place, and reconciles some enormously disparate opinions and techniques into a
coherent formulary.

From procedures for ultra-light duty tanks that use the absolute minimum of material, to tanks buildable by native women with no construction experience, to detailed procedures for building large tanks to last a lifetime?you can glean the best approach for your context.

In the do-it-yourself, innovative spirit of ferrocement, this appendix gives you not only recipes but numerous variations and ideas for promising innovations, so that you can follow a recipe or concoct your own to suit:

• Plans for Jumbo Thai Jar, an 800 gal (3 m^3 ) light-duty cistern, which can be adapted to make containers of this shape from 250-800 gal (1-3 m^3 ).
• Description of ultra light-duty ferrocement for cisterns up to 3000 gal (11 m^3 ) in size in the non-industrialized world.
• Plans for light-duty ferrocement 10,000 gal (38 m^3 ) cistern, adaptable for inexpensive, non-industrialized nation-style cisterns from 500-10,000 gal (1.9-38 m^3 ).
• Construction photos of medium-duty, urn-shaped, ferrocement cistern of 3500 gal (13 m^3 ), which can be used in conjunction with the heavy-duty ferrocement construction plan to guide the
  construction of medium-duty construction cisterns from 500-15,000
  gal (1.9-57 m^3 ). These also illustrate how ferrocement can be used to make creative shapes and details.
• Detailed plans for heavy-duty ferrocement construction of a 30,000 gal (110 m^3 ) cistern, which can be adapted to tanks from 3000-30,000 gal (11-110 m^3 ) capacity, and with the aid of an
  engineer, tanks up to 100,000 gal (380 m^3 ).

Sample Figures & Photos

Living Pond with aquatic plants, for wildlife habitat, swimming, water storage for irrigationat the Institute for Solar Living

Natural rock-shaped, stone colored, ferro-cement tank

Common features of water tanks

Aquifer, Well, and Spring Types

Drain Option Construction Details

Low tech drain and outlet for mortared stone water tank

Retrofit of a plastic tank with a sloped floor, sump, and dedicated drain

Multiple tank plumbing options