Water pump: types, sizing and what to check

What a water pump does in a house

In a house, a water pump does one of two jobs. It lifts water from a source below, such as a ground tank, a well or a borehole, up to a roof tank or straight to the taps. Or it boosts the pressure in the pipes so that showers and upper floors get a usable flow. Both jobs use the same two numbers, flow and head, explained below.

Types of water pumps

Types of water pumps

Type	How it works	Example in a maker’s data
Surface pump (peripheral or centrifugal)	stands beside the tank or well and draws water up through a suction pipe	Pedrollo PK: clean water, domestic use, suction lift up to 8 m
Submersible borehole pump	sits under water inside the borehole and pushes water up	Pedrollo 4SR: 4-inch borehole pumps for clean water
Pressure pump (booster) with pressure tank	a surface pump with a pressure tank and switch, so the pump stops and starts with demand	Pedrollo PK, which its maker pairs with small pressure tanks

Sources: the Pedrollo PK data sheet and the Pedrollo 4SR page.

A pressure tank is what turns a pump into an automatic water pressure pump for home use. As the Alberta Agriculture guide to pressure tanks explains, it keeps the system under pressure while the pump is off, and the tank should be large enough that the pump starts no more than 25 times an hour.

Reading a pump’s data: flow, head and power

Every pump has a curve that trades flow against head. Head is the height, in metres, the pump can push water; flow is how much it delivers, in litres per minute. The Pedrollo PK data sheet shows the trade-off for its smallest model, the PKm 60:

Reading a pump’s data: flow, head and power

Flow	0 L/min	10 L/min	20 L/min	30 L/min	40 L/min
Head	40 m	33.5 m	24 m	15 m	5 m

So the same pump that delivers 40 L/min against 5 m of head gives 10 L/min against 33.5 m. Pick a pump by the flow you need at the head you need, not by its maximum head.

Power is listed in kilowatts and horsepower side by side. The PKm 60 is 0.37 kW, sold as a 0.5 hp water pump, which puts one horsepower at about 0.74 kW. By that ratio, a submersible water pump of 1.5 hp has a motor of about 1.1 kW (our calculation).

Choosing a water pump

1. Where is the water? If its level is within the suction lift of a surface pump, up to 8 m for the Pedrollo PK, a surface pump can work. Deeper water calls for a submersible pump or deep water well pump in the borehole.
2. How high must it go? Add the height from the water level to the highest outlet, plus an allowance for pipe friction, and read the flow the pump gives at that head on its curve.
3. Does it need to run automatically? For steady pressure at the taps, use a pressure pump or booster pump with a pressure tank sized to the 25-starts-an-hour limit.
4. Where does it feed? A pump that fills a roof tank works with gravity supply; see water tanks for tank types and sizes.

What to check when you buy a water pump

1. Clean water only? Both Pedrollo ranges above are rated for clean water. The 4SR page sets a sand limit of 150 g/m³ for the 4SR-N and 200 g/m³ for the 4SR-S.
2. Working pressure. The PK data sheet gives 6 bar as the maximum working pressure of the PK 60.
3. Temperature. The 4SR is rated for water up to +40°C.
4. Depth. The 4SR may be submerged up to 200 m with a 4PD motor or 300 m with a 4PS motor.
5. The curve and its tolerance. Pedrollo states its curves to EN ISO 9906 Grade 3B; ask other makers which standard theirs follow.

Water pump prices and brands in Tanzania

The Pedrollo range is described under Pedrollo water pumps. Prices that Tanzanian sellers show for surface, submersible and engine pumps are tabled, with the date of each check, on water pump prices in Tanzania. Kitovu does not sell water pumps.