Shade or sun
A black tank in full sun hits 35 to 40 degrees Celsius inside by midsummer. Warm water grows algae. Even an opaque tank leaks light at the inlet screen, the overflow, the fittings. That is enough.
Shade fixes most of it. A shaded tank runs 10 to 15 degrees cooler in the same climate. That gap is the line between green sludge and clear water you can pour through a mesh screen onto the garden.
No natural shade. Pick light colours. White, beige, light grey reflect more than black or dark green. Insulating jackets exist. They are rarely worth the cost if you can park the tank in a building shadow.
Warm water also tastes flat. Households notice within a week.
The trees. A canopy works but drops leaves into your gutters and branches onto your roof. Add leaf guards. Inspect twice a year. Deciduous trees are the smart compromise: shade in summer when algae threatens, sun in winter when it does not.
Elevation buys pressure
Every metre of head gives you about 0.1 bar, or 1.42 psi. That is the whole physics of gravity-fed systems. A tank base at 3 metres delivers 0.3 bar at the outlet. Enough to run drip irrigation without a pump.
A ground-level tank delivers nothing. You buy a pump, you buy power, you buy a part that breaks.
On slopes the answer is obvious. Highest practical point. Let gravity work for free.
On flat ground you build a stand. Timber or steel, 2 to 3 metres tall, engineered for the load. A full 5,000 litre tank weighs 5 tonnes. The stand posts need concrete pads on stable footings. Stands sinking into soft ground after winter rain is the classic failure mode.
The trade-off
Height fights proximity. A tank at the top of the slope is far from the downspout. Long gutter runs lose efficiency. A tank beside the house is easy to plumb and gives you no pressure.
Compromise. Place it as high as the gutter run allows. If the high point is far from the roof, use a small header tank fed by a pump from a larger ground-level collector. Best of both.
Footings and access
In the Southern Hemisphere, the south wall sees the least direct sun. North wall in the Northern. East-facing gets soft morning sun and afternoon shade. West-facing cooks for hours after noon. Avoid west unless you can add a fence or planting to break the angle.
A 10,000 litre tank on a 2 by 2 metre footprint loads the ground at 25 kN per square metre. Soft clay and fill will not hold that. The pad must be level to within a few millimetres, compacted, and stable for decades.
Standard base: 100 mm of compacted crushed rock over geotextile fabric. Concrete slab is better. It costs more.
Leave 600 mm of clearance on the access side. You need to reach the inlet screen, the overflow fitting, the drain valve. A tank crammed between fence and wall fits today and becomes a misery the first time sediment needs flushing.
Multiple tanks and overflow
One big tank is cheapest per litre. Two smaller tanks fit awkward sites, feed different zones from different downspouts, and back each other up if one fails. They also let you isolate a tank for cleaning without losing the whole supply.
Plumb them in series. The first fills to overflow, then feeds the second. The highest tank always fills first, so your best gravity pressure is always available.
The last tank in the chain overflows to a swale, a rain garden, or a tree basin. Never to the storm drain.
Overflow is the part everyone forgets. A full tank in heavy rain can dump thousands of litres an hour. Hit bare ground next to the pad and you erode the footing within one season. Run the overflow at least 2 metres out, onto rock, into a gravel pit, or into a vegetated infiltration area.
Good overflow management treats the excess as the start of a second water-harvesting system, not waste.
See also
- Tank Sizing. Working out how much storage your roof and rainfall actually justify.
- Gravity-Fed Systems. Pressureless distribution from elevated tanks.
- Overflow Management. Sending excess water into the landscape, not the drain.
- Rainwater Harvesting Basics. The full chain from roof to storage.
- Catchment Calculation. Sizing the roof area that feeds the tank.