Security

Water security when the municipal supply fails

Municipal water cuts are not emergencies in South Africa — they are a recurring condition. The question is not whether your supply will be interrupted but how long you can last when it is.

David Watts · Filed under Security

How much water do you actually need to store?

The figure most people use — 50 litres per person per day — comes from humanitarian emergency guidelines. It covers drinking, cooking, and basic hygiene but not laundry, garden irrigation, or livestock. For a household that wants to function normally through a five-day interruption, 100 litres per person per day is a more honest target. That means a family of four needs 2,000 litres on hand before a cut starts.

Five days is not pessimistic. Municipalities with ageing infrastructure regularly log interruptions of three to seven days, and a burst main during a heat wave can stretch longer. If you also rely on stored water for a vegetable garden or small animals, add that volume separately — do not borrow from your drinking buffer.

Household size	3-day buffer (litres)	5-day buffer (litres)	7-day buffer (litres)
1 person (basic)	150	250	350
2 people (basic)	300	500	700
4 people (basic)	600	1 000	1 400
4 people (functional)	1 200	2 000	2 800
4 people + garden/animals	2 000	3 500	5 000
B	a	s	i	c		=		d	r	i	n	k	i	n	g	,		c	o	o	k	i	n	g	,		h	y	g	i	e	n	e		o	n	l	y	.		F	u	n	c	t	i	o	n	a	l		=		n	o	r	m	a	l		h	o	u	s	e	h	o	l	d		u	s	e	.

Standard Jo-Jo or polyethylene tanks in South Africa are sold in common sizes: 500 l, 1 000 l, 2 500 l, and 5 000 l. Two 1 000 l tanks are often easier to position and cheaper to replace than a single 2 500 l tank, and they give you redundancy if one develops a fault.

Gravity versus pumped — and the load-shedding trap

Most houses are plumbed on municipal pressure: water arrives at the meter under mains pressure and serves the entire house. When you add your own storage, you face a choice about how to move that water from tank to tap.

A pumped system uses a pressure pump to pull water from a ground-level tank and push it through the existing plumbing. It is the easiest retrofit because it requires almost no changes to your pipes. The catch is power. Pressure pumps are not low-draw devices — a modest 0.75 kW pump running for two hours a day is 1.5 kWh, which is meaningful on a small inverter battery bank. More critically, the pump fails the moment load-shedding starts, which in South Africa is precisely when a municipal interruption is most likely to compound. A power cut and a water cut at the same time is not a coincidence; both are symptoms of the same infrastructure stress.

A gravity system raises the tank above the highest point you need to serve — typically 3 to 5 metres above the roof line, or at a minimum above the highest outlet in the house. No pump, no power dependency, no failure mode during load-shedding. The trade-off is pressure: at 3 metres of head you get roughly 0.3 bar, which is enough for a shower rose and a tap but not for a high-pressure spray nozzle or some instantaneous gas geysers that require inlet pressure above 0.5 bar. Check your appliances before committing to the height.

A hybrid approach — gravity feed from a raised tank for the house, with a small booster pump only for appliances that need higher pressure — keeps your base supply power-independent while still serving demanding fixtures. The booster can run off a battery inverter without the load of supplying the whole house.

Tank placement and working pressure

For gravity feed, the usable pressure at the tap equals 0.1 bar per metre of vertical height between the water surface in the tank and the outlet. A tank with its water surface 5 metres above the shower head gives 0.5 bar — adequate for most domestic use. A tank only 1 metre above the outlet gives 0.1 bar, which is barely a trickle.

The tank stand must be engineered for the load. A full 2 500 l tank weighs 2 500 kg. That is not a job for untreated timber or a repurposed steel frame. A purpose-built bolted steel stand or a reinforced concrete plinth is the correct structure. If the tank is elevated on a roof, the roof structure must be assessed — this is not an assumption to make.

Position the tank where it can be filled from the municipal supply line (or from a rainwater or borehole system if you have one) without requiring a separate pump to top it up. A ball valve and float combination on the inlet means the tank fills automatically when municipal pressure returns, just as a toilet cistern does. This is the single most useful detail in a gravity system: you do not need to remember to fill it.

Shade the tank wherever possible. Direct sun heats the water, accelerates bacterial growth, and degrades the polyethylene over time. A north-facing wall or a shade structure adds years to the tank's life and keeps the water cooler.

Keeping stored water potable

Municipal water arriving at your tank already contains residual chlorine, which dissipates within a few days once the water is static. After roughly a week in a sealed tank, that residual is gone and the water is vulnerable to bacterial growth, particularly if the tank has any light penetration or the water has warmed up.

The standard maintenance approach is chlorination at the point of storage. Pool-grade granular calcium hypochlorite (65–70% available chlorine) is inexpensive, stable in sealed storage, and widely available in South Africa. The target residual in a sealed tank is 0.2 to 0.5 mg/l — enough to suppress bacterial growth without making the water unpleasant to drink.

Tank size (litres)	Calcium hypochlorite (65%) to add	Resulting residual (approx)	Reapply after
500	0.4 g (a level quarter teaspoon)	0.5 mg/l	7–10 days if sealed
1 000	0.75 g (a level half teaspoon)	0.5 mg/l	7–10 days if sealed
2 500	2 g (a rounded teaspoon)	0.5 mg/l	7–10 days if sealed
5 000	4 g (two rounded teaspoons)	0.5 mg/l	7–10 days if sealed
T	h	e	s	e		f	i	g	u	r	e	s		a	s	s	u	m	e		c	l	e	a	n		m	u	n	i	c	i	p	a	l		w	a	t	e	r		a	s		i	n	p	u	t	.		T	u	r	b	i	d		o	r		v	i	s	u	a	l	l	y		d	i	r	t	y		w	a	t	e	r		m	u	s	t		b	e		f	i	l	t	e	r	e	d		b	e	f	o	r	e		c	h	l	o	r	i	n	a	t	i	o	n	.		D	o	s	e	s		a	r	e		a	p	p	r	o	x	i	m	a	t	e		—		a		p	o	o	l		t	e	s	t		k	i	t		c	o	s	t	s		u	n	d	e	r		R	5	0		a	n	d		r	e	m	o	v	e	s		t	h	e		g	u	e	s	s	w	o	r	k	.

Granular hypochlorite must be dissolved in a cup of water before adding to the tank — never poured in dry. Stir, then wait 30 minutes before drawing water. Store the hypochlorite in a sealed container away from heat and direct light; it degrades quickly once opened and exposed to air.

For households that object to chlorine taste, a whole-house carbon filter on the outlet handles the flavour without removing the protection. The filter does not replace chlorination — it addresses the taste of a correctly treated supply.

If the water is to be used for drinking only and the tank is small, boiling remains the most reliable sterilisation method and requires no chemical management. For larger stores that serve the whole house, chlorination is more practical.

What people get wrong

The most common mistake is buying a tank and placing it at ground level, connected to a pressure pump, without any consideration of what happens when the power goes off. The tank is full, the water is there, and nothing comes out of the tap. People discover this at night during a simultaneous load-shedding and water outage, which is the scenario the whole system was meant to address.

The second mistake is undersizing. A 500 l tank feels substantial until a household of four runs through it in a day and a half. The sizing table above exists because the number needs to be worked out before the tank is bought, not after the first interruption.

The third mistake is ignoring water quality in the tank. A tank bought, filled, and forgotten for three months is not a water supply — it is a bacterial culture. Potability requires either regular turnover (using and refilling the tank continuously so water never sits long) or active chlorination. A tank that refills automatically from the municipal line every time pressure returns achieves turnover without effort; a tank that is filled once and sealed does not.

The fourth mistake is connecting stored water directly back into the municipal reticulation without a non-return valve or air break. This is illegal under most municipal bylaws and can contaminate the mains supply for neighbouring properties. The stored supply must be physically separated from the municipal line, or protected by a correctly rated backflow preventer.

What we would do differently

• Calculate the storage target before buying anything: number of people × 100 l × number of days, plus any livestock or garden allowance.
• Choose a raised gravity system as the primary supply, sized so that the bottom 20% of the tank (the unavoidable dead zone and residual) does not eat into the usable buffer.
• Install a ball-valve and float inlet so the tank refills automatically from municipal pressure without any action needed.
• Add a non-return valve between the municipal supply line and the tank inlet — this is not optional; it is a legal requirement in most municipalities.
• Shade the tank on the north and west faces, or orient it against a shaded wall.
• Begin a chlorination routine from day one: dose, test with a basic pool kit, record the date, and reapply on a seven-day cycle if the water is not turning over.
• If a pressure pump is used, wire it to the battery inverter rather than the mains, so it survives load-shedding at least for the duration of the battery bank.
• Treat the first 500 l of gravity storage as the irreducible minimum and add capacity once the gravity system is running — not before.

Is it worth it?

For most South African households, some form of water storage is no longer optional. The question is only how much and in what form. A 1 000 l raised tank with a float valve costs a morning of work to install and gives a family of four three to four days of basic supply without touching a switch or a pump. That is a measurable improvement in resilience for a modest outlay.

Where it becomes more complex is the transition from a basic buffer to a full gravity-fed household system. Elevated tank stands, roof load assessments, and plumbing modifications add both cost and planning. For those steps, the value depends heavily on how often and how long your specific municipality cuts supply — and that varies enough between areas that a general answer is not honest.

What we can say is that the load-shedding and water-outage overlap is not going away. A pumped system that fails at night during stage 4 is a real scenario, not a theoretical one, and the cost of not designing around it is measured in the hours — or days — you spend carrying water.

The cheapest useful first step is a single 1 000 l tank elevated on a purpose-built stand with a float valve inlet and a basic chlorination routine. Everything after that — additional capacity, filters, booster pumps for high-pressure appliances — builds on that foundation rather than replacing it.