No, you don’t need one, but you may want one. This article goes into detail about what the role of a headertank is and why you might (or might not) want one.
The role of a headertank in a rainwater harvesting system is to hold some of the stored water, from the main rainwater harvesting tank, above the appliances so it can be gravity fed down through the house. The water from the main tank is transferred to the headertank using a pump.
Mains water is also connected to the headertank, if there is no rainwater in the main (underground) tank, mains water will feed the headertank allowing for uninterrupted water supply to the appliances.
Yes, you don’t necessarily need a headertank in every rainwater harvesting system. Water can be pumped directly to the toilets and appliances. This is called a “direct feed” system. With a direct feed system a mains water top up is supplied so a small amount of mains water can be sent back to the main rainwater tank in the event it is running dry. This keeps the supply of water to appliances uninterrupted in the event of a dry spell.
There are a couple of things you should look out for when buying a headertank system.
Then you can install a direct feed system pumping water directly to the appliances.
You shouldn’t use a headertank in a bungalow or if your kitchen is on the top floor. This is because the gravity pressure may not be good enough from the headertank to supply the washing machine. The higher up the headertank the better the pressure will be. If you don’t have at least one floor between your headertank and washing machine, then consider a direct feed system.