Well, the Coarse Aggregate together with the hollow blocks and Coarse sand is not for he ferrocement but for the basement and foundation.

my question "says who?" is rhetorical and the academic discussion of a "ferro cement" tank is useless. this is Thailand! anybody who was involved in Thailand building a home will laugh out loudly when looking at the UNHCR instructions.

no aggregate = crumble like a mole hill!

Hmmm, the stuff hold our bricks together does not contain aggregate, and it's bloody hard.

Lots of people have built boats using this material, and obviously UNHCR seem to think it works OK.

You use aggregate in foundations and supports and the stuff that holds your bricks together is mortar which is made up of washed sand and cement

A round concrete water tank is stronger than a square or retanguler one whatever one you build you need to design it that you have an access via the comcrete roof should you ever find the need to have to climb into it please also consider overflow pipes as well as the ball and cock system all this can be done underground with the only section showing would be the metal entrance hatch plenty of steel and aggregate in the concrete will do the trick finished of with polished waterproof cement on the interior of the tank. I would also make sure that you can ciculate the stored water. I always put a very small amount of chlorine in my water tank .

We built an above ground tank 6m diameter X 2.5m high entirely with ferro cement technique and there are at least 4 others up here in Pai of similar style with domed roofs with no problems for years. As mentioned ferro cement technique has a long history in boat building and is very cost effective.

Good idea about using plastic lining for an underground tank.

An excellent DIY reference is "Water Storage - tanks, cisterns, aquifers and ponds" by Art Ludwig, published by Oasis Design.

I had the pool builder do my tank (50,000 liters) at the same time as he built the pool. It actually forms the floor of the pool pump house which is built on top of it. As Naam suggests, I think you are far ahead with an inground tank for both the stress reasons and not having to have such an unsightly bunker sitting in the middle of your garden. I use a dual Hitachi 300 pump setup to draw the water and supply pressure to the house. The tank is slightly over 3 meters deep and a standard pump works fine, no need for the "deep" pump type.

One note, unless you are VERY conservative with water or you get a quite constant amount of rainfall, don't think that 50,000 liters will last 6 months. In Hua Hin, where we go months without a drop of rain 50,000 litres lasts about 6 weeks and that is without garden watering. That is for pool topups, and household use only.

Not sure why one poster said to circulate the water, on the contrary you want the water to settle so all the solids are on the bottom and your pump suction is placed 6 inchs or so off the bottom. No need to worry about algae growth as long as no light can reach the water. Although I do also throw a swimming pool chlorine puck in the tank just to take care of the "bugs" :-)

Coarse Sand for Basement m3 14 21 25

Hollow Blocks pieces 150 280 195

Cement kg 3267 4553 5072

Fine Sand m3 4.26 6.0 7.0

Coarse Aggregate m3 5.0 7.0 8.14

OK, Ok, you win, but I never said it was cement. However your own quote of the UNHCR document does NOT mention fine aggregate does it?

The building system is called Ferro Cement, even though it is incorrectly named as such (blame Joseph Monier for that), it's not really concrete either is it as it does not contain coarse aggregate, just sand and cement more like steel reinforced mortar.

Ferrocement is fine sand and cement WITH a ingredient called POT ASH....Thats what make it watertight and lightweight for making boats. You will need POT ASH to do a good seal. Talk to the suppliers to the Oil Rigs etc etc, they supply this to the field for drilling....Put epoxy resin over the surface on the inside, after the cement has cured....it will outlast you and your kids.

cheap underground , build pond like , with pvc or hdpe foil with concrete slabs on top for the cheapest . The plans from UNHCR are 2nd cheapest , a swimming pool construction is by far the most expensive .

Your small post pretty much says it all. I received a price quote for a swimming pool type for 500K baht. Now I am trying to think of a reason not to use the first option -- pvc/hdpe foil with concrete floor panels over it. Any idea where liners of this size could be found?

Well Canopy someone is ripping you off.........I had mine done for 180,000 baht.

Not pretty, but could be visually screened-off. I'd think the cheapest solution would be a prefab, plastic lined, above-ground swimming pool with cover.

If you go underground in a clayey soil type, make sure your structural engineer pays mind to the water table so you don't 'float your concrete/ferro cement/gunnite boat" if it gets a bit empty and the water table is above the tank bottom.