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Water Storage Tanks

Should you install a water tank?

Do you need a water tank, which type of tank is best, concrete plastic or steel and what size will you need. It can be very useful to have a water storage tank so what are the advantages and disadvantages.

Why do I need a Water Tank?

5,000 litre polyethylene water storage tank

We tend to take our supply of water for granted don't we, unless we have trouble with the supply.

Some of us have a government water supply which for some of us, unfortunately, can be very variable. Some people report no problems and a steady pressure while others are not so lucky.

One woman I know with a government supply had water pressure that varied from being so strong it was bursting flexible pipe couplings to as so weak it was just a dribble. Sadly the dribble was when she needed it most – in the morning when everyone else was taking a shower.

For the majority of us who don't have a government supply it is the old water pump and bore (or well) setup.

Either way in the past it was common practice to use a water tank to act as a buffer to protect our domestic needs from the vagaries of wells, pumps and those ever so dedicated people of government and of course teh electric company.

These days many people don't bother with water tanks, they like the convenience of the automatic water pump.

It goes something like this. You turn on the shower which immediately releases the water pressure in the pipe, a pressure switch senses the loss of pressure and switches on the water pump which pulls water directly from your well or bore and pumps it down the line to the shower head. When you have finished you turn the shower off, the pump keeps on pumping for a split second and the water pressure builds up in the now closed pipe until a second pressure switch senses the higher pressure and switches the water off allowing you to gambol around trying to find your towel.

All well and good, very convenient but this system has two fundamental flaws.

Firstly if the pump is not set properly or if it is too large your shower will be a bit of a hit and miss affair.

Secondly if the power goes off - no water.

You know you can't beat a tank. I've got one. It sits at the top of a 5 metre high post and I don't even know it's there. I never have to get up there to sort it out – a can't there's no ladder BUT I know it's there because:

  1. I always have water even in a power cut and
  2. My water is always the same even pressure.

What Type of Tank Should You Have?

If we look back we find that the old Dutch colonialists knew what they were doing. Look around and you will note that old houses nearly always have a tower with a tank on the top. Usually they were concrete boxes supported by four concrete columns and with a roof over the top to keep out birds and other things. These old concrete tanks are surprisingly reliable and don't seem to leak very often. Many people put a plastic or steel tank inside the old concrete one.

These days people tend to use concrete, stainless steel or plastic for tanks. Each is effective but has its own problems.


Concrete tanks are brittle and may crack if they are not built properly or the steel reinforcing rusts (yes they should be reinforced). These days concrete tends to be used for underground water storage tanks.


Plastic tanks allow light in so the water gets dirty but worse they deteriorate in sunlight. The sun's ultra violet rays attack and breakdown the polymer chains in the plastic which is weakened and cracks. You can easily tell when a plastic tank is damaged because its colour fades as the plastic deteriorates.

Stainless Steel

Stainless steel is theoretically the best material but beware - stainless tanks are made from low grade 304 stainless steel. 304 is officially graded as “just a teeny weeny bit stainless on a good day” as opposed to marine grade 316 which is officially graded as “really, really impressively good stainless steel that wouldn't rust if it was peed on for a year by a thousand elephants”. A stainless steel tank, depending on the chemical balance of your water, can rust through in as little as 3 months. Mine, on the other hand, has sat up that pole for the past five years at least and shows no sign of deterioration. Life depends on how saline the water is.

How big a water tank do I need?

The standard size for most houses is 750 to 1,000 litres (that is a metric ton in weight!). Small 1-2 person households can manage with a 500 litre tank. Over three bathrooms and you may need to consider a second tank depending how dirty your guests they are.

How high a tank tower?

The key factor when considering a water tank is water pressure. The height of the surface of the water in the tank above the shower head determines the pressure of water at the nozzle. As the diving fraternity readily know 10 metres of height difference increases water pressure by 1 atmosphere or 14.7 psi (pounds per square inch). 10 metres is the height of many water tanks. Mine is only 6 metres from the ground to water level giving me 8.8 psi but it is quite satisfactory for my needs.

There is a legal building height limit in Bali of 15 metres (the height of a palm tree) so theoretically the maximum water pressure from a tank is around 1.3 atmospheres (15 metres less the 2 metres to the shower head) giving you 19 psi.

Note that if you have one of these fancy shower heads that can do everything from massaging your shoulders to knitting you a jumper you may need more pressure than my rather simplistic needs of merely washing myself. Also if you are supplying water up to a second floor this will require additional pressure.

If you do need more pressure than your tank can supply you will need a pump after the tank to boost the water pressure. Water pumps are usually set to switch in at around 20 psi and cut off at around 40 psi. For this purpose a small pump will do and, in many respects, is better than a large pump. We'll go into this another time.

Water Flow

These days many people are going for “rain effect” showerheads. Unfortunately they take more water than a fireman's hose to work properly and it is important to consider the issue of getting enough flow of water. The pipework must be large enough diameter to carry the water you need. It is advisable to install a pressure pump if you are running a rain effect showerhead. Even better - be considerate of the impending water shortage in Bali and throw the thing in the bin.

Dirty Tanks

Tanks can get dirty either from dirty water or from sunlight which encourages algae to grow (like a green swimming pool). It is a good idea to make sure you can drain the tank without having to empty it through your shower so you can clean it regularly. The best way of keeping the water clean is to use it all the time and so keep the water changing.

A couple of tank tips:

If you have a concrete tank it is also a good idea to put a piece of Kalsiboard (cement based fibre board) across the top. This will do two things, it will keep the sun off the water to stop it growing fresh vegetables and it will also stop the birds leaving little presents in it. If you have a plastic or stainless steel tank make sure it has a top on it.

If you have a plastic tank paint it. This will do two things. It will reduce the sunlight inside the tank so reducing algae growth and it will protect the plastic from ultra violet light thereby considerably extending its life. Any old paint will do although it is best to use water based emulsion as this will not react with the plastic.

You may have heard of a bar. A bar is a unit of pressure, 1 atmosphere = 1.01 bar.

Copyright © Phil Wilson October 2009
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