Propertyzone's borehole compliance and geology articles tell you how to get a borehole right and legal. This article takes the next step: how to design a home water system that combines borehole supply, rainwater harvesting, and storage capacity so that a Harare household can function through the water supply failures that are now a routine planning assumption. The component costs and design choices are specific to Harare's infrastructure reality.
Every water system in Harare fails for a different reason and at a different time. A borehole solves the municipal intermittency problem but not the borehole failure problem: pumps burn out, yields drop during dry spells, and a mechanical fault leaves the house with nothing. A large storage tank solves the intermittency problem but drains in three days if the borehole is down and the municipality is not supplying. Rainwater harvesting supplements both, but delivers zero input for six months of the year when Harare's dry season produces essentially no rain. A system that integrates all three, sized correctly for the household and sequenced correctly in the plumbing, gives a family functional independence from the municipal supply for months at a time. No single component achieves that. All three together do.
This article covers the design and cost of each component and how they connect into a working integrated system. For borehole geology, ZINWA permit requirements, drilling costs, and compliance detail, see the Harare borehole geology guide and the borehole compliance and permit guide. This article begins where those end.
Before sizing any component, you need to understand the single most important constraint on Harare's rainwater harvesting potential: five months of the year produce almost no rain at all.
Harare's rainfall averages 830mm annually, but it arrives in a distinct wet season from November to March. The monthly distribution from 30-year climate averages runs approximately as follows.
| Month | Average Rainfall (mm) | Useful for Harvesting? |
|---|---|---|
| January | 212 | Yes, peak month |
| February | 182 | Yes |
| March | 90 | Yes, tapering |
| April | 31 | Marginal |
| May | 8 | Effectively no |
| June | 2 | No |
| July | 3 | No |
| August | 1.4 | No |
| September | 5 | No |
| October | 23 | Marginal, transitional |
| November | 100 | Yes, season starts |
| December | 114 | Yes |
From May to September, five consecutive months, a Harare roof collects almost nothing. A household that relies on rainwater harvesting as its primary supplement must carry enough stored water from the March/April rains to bridge to November. For a family of four consuming 600 litres per day, that five-month gap requires 90,000 litres in storage to replace rainwater entirely. No residential rainwater system is sized for that. Rainwater harvesting in Harare is a wet-season supplement, not a year-round substitute. Design your system with that constraint as the starting point, not an afterthought.
The borehole's role in an integrated system is to be the primary supply source when municipal supply is absent, which in much of Harare is most of the time. The pump specification and the rising main design determine how effectively the borehole feeds the storage system.
Submersible pump selection. For residential boreholes in the 30 to 60 metre depth range typical of Harare's northern suburbs, a 0.75kW to 1.5kW submersible pump is the standard specification. The pump must match the borehole's yield. A pump rated to extract 1,500 litres per hour from a borehole yielding 600 litres per hour will run the borehole dry and cavitate the pump. Get the driller's yield test result before specifying the pump. If the yield report is not available, treat the pump as over-specified until proven otherwise.
The rising main. The rising main is the pipe from the submersible pump to the surface. Standard sizing for residential boreholes is 25mm to 32mm HDPE or uPVC. The rising main connects to the distribution pipework that fills the ground-level storage tank. This connection point should include a non-return valve to prevent backflow down the rising main when the pump is off, which would lose the water column and extend the next pump startup cycle.
Controller and protection. A pump controller protects the motor from dry-run damage, voltage fluctuations, and phase failure. In Harare's ZESA environment, where voltage instability accompanies every load shedding transition, a controller is not optional. Solar-powered borehole pump systems, which are increasingly common in Harare, use a separate solar pump controller designed to match panel output to pump demand. See the solar power guide for pump load sizing in a solar system context.
Header tank versus ground-level tank as the primary borehole destination. The borehole pump should fill a ground-level storage tank, not a header tank directly. The reason is simple: a ground-level tank can hold 5,000 to 10,000 litres or more. A header tank is typically 500 to 2,000 litres. Filling a small header tank directly from the borehole means the pump cycles on and off constantly as the header empties and refills, shortening pump life. The correct sequence is: borehole fills ground tank, a separate pressure or float pump fills the header tank from the ground tank, and the house draws from the header tank under gravity.
Rainwater harvesting captures rain falling on your roof and diverts it, after filtering, into the ground-level storage tank. It is a supplement, not a primary source. In the wet season it can meaningfully reduce borehole run hours and extend system autonomy. It requires three things to work correctly: properly functioning guttering, a first-flush diverter, and a correctly sized connection to the storage tank.
The first-flush diverter: why it is not optional. A roof surface between rain events accumulates dust, bird droppings, insect debris, and chemical oxidation from the roofing material itself. The first rain washes all of this into the gutters. Sending that first flush directly into a drinking-water storage tank contaminates the entire stored volume. A first-flush diverter is a passive pipe device installed on the downpipe before the tank inlet. It captures the first volume of roof runoff, typically 1 to 2 millimetres of rainfall per roof area, and diverts it to waste or to the garden. Only once the diverter chamber is full does water flow into the harvesting system.
For a 200m² roof, 1mm of rainfall generates 200 litres of runoff. A properly sized first-flush diverter for that roof captures and diverts the first 200 to 400 litres of each rain event before clean water enters the tank. The device is simple, passive, self-resetting between rain events, and costs between $20 and $80 in local plumbing market pricing. It is the most cost-effective component in the entire rainwater system and the one most commonly omitted on cheaper installations.
How much water your roof actually produces. Use this calculation for any roof:
Catchment volume (litres) = Roof area (m²) × Rainfall (mm) × 0.001 × Collection efficiency
Collection efficiency for a standard zinc or tile residential roof in good condition is approximately 0.70 to 0.80, accounting for losses to evaporation, overflow, and the first-flush diversion.
For a 200m² roof in Harare's wet season (November to March, approximately 698mm of the annual 830mm total):
200 × 698 × 0.001 × 0.70 = 97,720 litres
Over 151 days of November to March, that averages 647 litres per day. A family of four consuming 600 litres per day can theoretically be supplied entirely from rooftop harvesting during the wet season, provided the storage tank is large enough to absorb the sporadic nature of actual rainfall. In January alone (212mm), a 200m² roof at 70% efficiency produces approximately 29,680 litres, more than enough to fill a 10,000-litre tank twice over. The constraint is not the roof area or the rainfall. The constraint is storage.
Filtration. A sediment filter on the tank inlet line removes particulates that pass through the first-flush diverter. A 50-micron inline filter at the tank inlet is standard. This does not make the water safe to drink. Treatment for drinking is a separate step covered below.
The most common failure mode in Harare water systems is undersized storage. A 5,000-litre tank holds approximately 8 days of supply for a frugal family of four at 150 litres per person per day. Eight days sounds like a buffer until the borehole pump fails on a Friday, the replacement part is not in stock, and the municipality has not supplied in two weeks. At that point, eight days becomes an immediate crisis.
The autonomy calculation. Size your total accessible storage based on target autonomy, not on what fits conveniently in the yard.
| Household Size | Daily Consumption at 150L/person/day | 7-Day Autonomy Storage | 14-Day Autonomy Storage |
|---|---|---|---|
| 2 people | 300 litres | 2,100 litres | 4,200 litres |
| 4 people | 600 litres | 4,200 litres | 8,400 litres |
| 6 people | 900 litres | 6,300 litres | 12,600 litres |
| 8 people (extended family) | 1,200 litres | 8,400 litres | 16,800 litres |
For a family of four, a single 5,000-litre ground-level tank gives approximately 8 days of autonomy and that tank should be considered the minimum, not the target. Two 5,000-litre tanks, or one 10,000-litre tank, gives 16 days and is a more realistic buffer against both borehole failure and dry-season bridging.
Ground-level tank versus header tank. A ground-level tank holds volume. A header tank, mounted on a stand high enough to create gravity pressure to the house, delivers water without requiring a pump to run for every tap use. Both are needed in a well-designed system. The ground-level tank is the reservoir. The header tank, typically 500 to 2,000 litres, is the pressure vessel. A float switch in the header tank triggers the pressure pump when the header drops below a set level, refilling it from the ground tank. When ZESA is off and the solar system is not running the pump, the header tank continues to supply the house under gravity for as long as it holds water.
Tank materials available in Zimbabwe include food-grade HDPE polyethylene tanks from local manufacturers including DripTech (made in Harare) and JoJo-equivalent tanks available through ZBMS and Union Hardware Zimbabwe. Specify triple-layer construction: white food-grade inner layer for inspection, black middle layer to block algae-promoting sunlight, and UV-resistant outer layer. A 12-year manufacturer warranty is available on top-specification tanks. Do not buy a single-layer tank for any potable water storage application.
A correctly plumbed integrated system operates as follows.
Neither borehole water nor harvested rainwater is safe to drink without testing and treatment, regardless of what the water looks like or smells like. Research into Harare borehole water quality, including a 2024 NERC study of 21 Harare boreholes, found troubling contaminants at concentrations above safe drinking limits in multiple samples. Rainwater, even after first-flush diversion and sediment filtration, can carry biological contamination from bird droppings and atmospheric pollution.
UV sterilization is the most practical treatment method for residential use. A UV sterilizer installed on the outlet pipe from the ground tank kills bacteria and viruses at flow rates suitable for household use. UV units appropriate for residential flow rates are available in Harare and typically cost between $100 and $400 depending on flow capacity and brand. UV treatment does not remove chemical contaminants. If there is any reason to suspect chemical contamination in the borehole water, including proximity to industrial sites, petrol stations, or agricultural land, a water quality test from an accredited laboratory is required before drinking the water, and a carbon or reverse osmosis filter may be needed in addition to UV.
For the full borehole water testing protocol and required parameters, refer to the borehole compliance guide.
Water from the storage system that has not been treated through a UV unit or tested should be treated as non-potable and used only for garden irrigation, toilet flushing, car washing, and laundry.
The table below covers the storage and integration components of a complete system, excluding the borehole itself. For borehole drilling costs ($900 to $7,000 depending on depth and geology), refer to the borehole cost guide.
| Component | Specification | Estimated Cost (USD) |
|---|---|---|
| Ground-level storage tank (5,000L) | Food-grade HDPE, triple-layer, 12-year warranty | $250-$300 |
| Ground-level storage tank (10,000L) | Same specification | $500-$800 |
| Header tank (2,000L) + stand | Food-grade HDPE + steel stand at 2-3m height | $200-$400 |
| Rainwater first-flush diverter | Sized for 200m² roof catchment | $20-$80 |
| Rainwater sediment filter (inline) | 50-micron cartridge filter at tank inlet | $30-$80 |
| Guttering modification and downpipe diversion | Redirecting 1-2 downpipes to storage connection | $100-$300 |
| Borehole pump controller | Dry-run and voltage protection | $80-$200 |
| Float switches (ground tank + header tank) | Two units with wiring | $40-$120 |
| Pressure pump (ground tank to header tank) | 0.5-0.75kW centrifugal pump | $150-$350 |
| UV sterilizer (residential flow rate) | Sized for household consumption | $100-$400 |
| Integration pipework, valves, and fittings | HDPE or uPVC, non-return valves, isolators | $200-$500 |
| Labour (plumber + electrician) | System integration, wiring, commissioning | $200-$600 |
| Complete system total (exc. borehole) | 5,000L ground tank + 2,000L header + rainwater harvesting + UV + integration | $1,370-$3,330 |
| Complete system total (exc. borehole) | 10,000L ground tank + 2,000L header + rainwater harvesting + UV + integration | $1,620-$3,830 |
These are component-level estimates sourced from current Zimbabwe and regional plumbing supply pricing. Get itemised quotes from at least two local plumbers before committing. Labour rates in Harare vary significantly based on system complexity and the contractor's experience with integrated water systems specifically.
For cluster and sectional title properties, the cluster homes in Harare guide covers shared borehole and tank infrastructure arrangements that differ materially from freestanding residential systems. For apartments, the owning a flat in Harare guide addresses the constraints on individual water storage installations in strata title developments.
