Looking for rainwater catchment ideas & inspiration!

Hi! I've just been scrolling through several other rainwater catchment topics, and wondering if anyone would have specific ideas and suggestions for our case.

We live off the grid in the mountains of inland Spain - with solar panels for electricity and a borehole for water.
Twice a year, we get LOTS of water from the sky though - and we'd like to use that better.

We already have all the gutters from the main house (about 200 square meters, equals a little over 2000 square foot) converging in one point... "all we need" now, is to build a rainwater catchment system that will last us a lifetime (or at least, long). In time, we'd like to use it to fill up a natural swimming pool we're going to build a bit further down, to irrigate our olive trees, and to provide water for animals. And you never know, one day we might want to convert rainwater catchment into our main source of water in the house...

So we're thinking one big 50.000 liter (about 13k gallons) concrete tank. I'd like to place an extra barrel before the big tank - one that is easy to clean out, as a settlement tank.
I'm not yet quite sure how we could go about cleaning out that big tank when needed... would it be needed often?
Did anybody else here build a concrete water tank - what are your experiences with it?



This is a picture of the house, so you can see what I'm talking about...

The roof we're currently planning a rainwater catchment system for, is the top roof. For the smaller roof on the left (which is the roof of the guest bedrooms, we offer farm stay accommodations), we'll need to design a separate system... probably something more simple, and dug into the terrace.

I'd be thankful for any insights - opinions - pics of your own catchment projects - etc!

Check out Art Ludwig's book .  It shows you exactly how to build ferrocement tanks of the size you are talking about and answers your questions.  His instructions include a man hole and ladder so you can drain the tank and physically get in and clean the tank.  How often you need to clean it will likely depend on how clean the water coming in will be.  You will need a very large tank if you are getting infrequent rains.

Water Storage by Art Ludwig

Wow, that looks like a great resource - and exactly the thing we need. Thank you for the tip, I'll order it today!

I put in a concrete water tank (120k litres) in 2008 for about AUD $20,000

I'm happy with the decision.

Thoughts / suggestions:

I'd probably not do a 50kl tank, as that's only twice the capacity of two large plastic tanks (we have 5 of these around the place).  Compared to concrete, plastic tanks tend to be cheaper, you can split your water storage into different locations, and you can move them (not easy, but doable).  Obviously you'd need to run the prices locally -- I expect concrete tanks are cheaper in ES than AU.  (Everything's expensive in AU)

You say that you have lots of water twice a year - do you mean a couple of single events, or over a period of several weeks?  

I ask because placement is important, especially if you want to run irrigation from the tank using gravity.   Solar-pumps obviously don't work while it's raining, but if you've got battery capacity to move water uphill, I'd recommend putting whatever tanks you've got as high up your property as possible, particularly if you end up with a single large concrete tank.  It just opens up your options later.

Water cleanliness - I use a 2" mesh filter for water coming in.  I get water from a spearpoint at the river, which is 'mostly' clean, but has some iron salts (not going to be filtered by mesh), and some very fine grit/sand (mostly filtered by mesh).   I also have filters on the outlet pipes just before any irrigation gear, as I use gravity fed dribblers.   If you keep the tank sealed properly, and have a filter on the way in (if it's rainwater, then one of those 60 litre overflow gutter attachments work well), you shouldn't  need to clean it out very often.  (I haven't cleaned mine at all yet).   Remember that you can dredge out most tanks, without emptying them, and probably only lose a few hundred litres of water in the process.

You'll see with my tank the roof doesn't catch its own water (bit of a waste), and has grooves under which they put small foam plugs that fell out the first time it got windy.  I should have gone around and glued / foamed up all the gaps properly, but frogs and dust will probably always find a way in.

We have a 20.000 ltr plastic tank and they are ugly. I find metal ones much much nicer, but they can rust, usually they have a plastic liner. An open swimming pool for water storage is not very good because most of the water will evaporate. YUo will need a pump.

Jedd Rashbrooke wrote:
You say that you have lots of water twice a year - do you mean a couple of single events, or over a period of several weeks?  

I ask because placement is important, especially if you want to run irrigation from the tank using gravity.   Solar-pumps obviously don't work while it's raining, but if you've got battery capacity to move water uphill, I'd recommend putting whatever tanks you've got as high up your property as possible, particularly if you end up with a single large concrete tank.  It just opens up your options later.

I would recommend just the opposite, put the holding tank lower than the collection area, that way all you need is gravity to collect the water.

Pumps, batteries, etc. can fail, gravity never fails.  
With your idea, if the pumps fail during rainfall then you won't collect any water, and you can't use water you don't have.

If the holding tank is lower and the pump fails when distributing the water, well worse case you can still use buckets.  Plus you can spend a day repairing/replacing the pump with little to no harm done, the water will still be in the tank tomorrow.

Or you could put a smaller tank up high, and pump water up to it, maybe even a water tower.

Peter VanDerWal wrote:
With your idea, if the pumps fail during rainfall then you won't collect any water, and you can't use water you don't have.

You're absolutely right, and I should have been clearer.

I wasn't / wouldn't anticipate someone in this situation having a single tank - certainly they need a collecting tank sufficiently large to cope with water from the roofs of both the main and the guest structures during a rainfall event (hence my question about intensity and duration of the 'two rainy periods a year').

A header tank - if it's less than 20k litres - is probably more frustrating in terms of keeping it full (which is why in general I advocate large storage tanks at the top of the property) ... but naturally depends on the scale of the operation here.

Didn't see this until now, thank you for your thoughts Jedd!

I'm going to research the possibility of doing 2 plastic tanks... I actually didn't even think about that option. They'd be enormous tanks though, and would probably not have the shape that fits where it needs to fit... still, we could find a way around it!

Jedd Rashbrooke wrote:You say that you have lots of water twice a year - do you mean a couple of single events, or over a period of several weeks?

A bit of both - there's usually one or two torrential rains a year (one around the first of november, one in april or may). And in fall or spring, we also have "normal" rainfall (lots more than in winter or summer).
We do have battery capacity to move water uphill - especially in summer of course

I didn't consider the option of dredging without emptying, that's probably some sort of vacuum cleaner? Will look into that option as well.

Loving your system! We hadn't thought of having the tank roof catching its own water... thanks for the tip.

We'll at least have different tanks for the upper part of the house and the guest section... Hadn't considered the option of putting the bigger tank downhill though. We'd mostly require to pump it up in summer...

We have one plastic tank (for the water from our well), it is dead ugly indeed We built something around it (just a stone wall), we'd probably have to do that with the other one(s) as well.
The swimming pond would definitely not be for water storage... more to escape the Spanish heat in summer, and maybe add a few fun plants as well!

Lots of food for thought here, thank you Jedd & Peter & Angelika!

I think, in your situation, if I needed to use a pump somewhere in the process, it wouldn't be at the collection stage, where a mechanical failure might mean that I don't have the water I need to live, or to keep things alive on my property.

I would go with the larger collection tank at the bottom. I would make sure to have more capacity than I need, and I might even, if the ground isn't too rocky, sink it below grade.

I like to set things up in a fail-safe manner. It's one reason why my hydroponic or aeroponic systems are always hybrids, with the nutrient-adapted roots being held in cloth bags of real, living soil. If the pump or power fails, there's a natural backup that will last for the duration of the emergency.

This is also the reason, for instance, that I prefer a flood-and-drain bucket hydroponic system, that lends itself to the use of real, living soil, to a nutrient film technique or aeroponic approach, which almost exclusively rely on an uninterrupted power source for their pumps and/or sprayers.

You only get your water twice a year, from what you're saying. I don't think I would risk not being able to collect a half-year's allotment of water because my pump died. Gravity is your friend.

-CK

Thank you for your input Chris... Gravity is my friend indeed!
Having the first tank higher up (next to the house) would mean we can collect at least the water from the higher roof - and divide that to go to the animals and olive trees, further down. The second tank could go lower... not quite sure where yet though, as the ground is quite rocky - and we might need a full building permit if we want to build a cistern.
Lots of things to consider there

I went with a 22,500L poly settling tank slightly downhill and a ~120,000L concrete tank level with the house.  (Our property is pretty flat, so no option to put the concrete tank significantly higher.)

Placing the poly tank downhill means that the downpipes and transfer pipes are always 'dry'.  This is important if you only get water infrequently, as a 'wet' system will have water sitting in warm pipes for a long time and you'll have stagnant water in it between rain events.

The settling tank is poly because when organic sediment settles on the bottom, the anaerobic zone that will quickly form will be acidic, and that will eat the bottom out of a metal tank in no time at all (lucky to get 15 years out of them around here).

The settling tank is 22,500L because that is twice the capacity required to absorb the 'typical maximum annual' 24-hour rain event that we get.  There has been no rain event in recorded history (>100y) at this location that would fill that tank up in a single day.

Under normal circumstances it will rain a bit, the tank will fill up a few cm, then it will shine a bit, rain a bit, shine a bit...  I have an external water level indicator that can easily be seen from the house.  If the seven day weather forecast is predicting a lot of rain, and the water level in the tank is too high for my liking, I manually trigger a pump which pumps water from the clean layer of the settling tank via a 50mm underground pipe, uphill to the concrete tank about 100m away.  We haven't been in the new place that long, and rain is a variable thing, but so far we're talking about four or five pumping events per year.

It's best to leave water in the settling tank as long as possible... so things have time to settle.  The longer you can leave it in there, the cleaner the water that you pump out will be.

I've yet to find a system that can do this (integrate weather forecasts, water levels and settling time to maximise water quality) automatically, so it's a manual process for now.

The main tank is concrete because concrete helps neutralise acidic water and results in better tasting water (at least according to my senses).  The main tank is ~120,000L because that's about a year worth of domestic water consumption for the whole house (with no effort made to conserve water).  It's a good hedge against drought.  Also the $/L cost of concrete storage is better than steel around here once tanks get above the ~80,000L mark, so it ended up cheaper for the amount of storage we wanted/needed.

A variable speed (constant pressure) pump connected to the concrete tank means we can open up to 3 taps at the same time and get a consistent 500kPa at — 11L/min out of — each of them.  Really nice for a house with two bathrooms.

tl;dr:  As others have also commented, a downhill collection/sediment tank is great because gravity never fails — even if you do nothing, you'll still collect the water when it rains.  A big collection/settling tank buys you time to let it settle and pump it out at a convenient time.  Poly means it lasts longer.  Large concrete main/storage tanks are cheaper and produce better tasting water.  YMMV.

Have a look at this topic Benefits of rainwater collection

Its where I am sharing my knowledge and skills from Australia

I can say settlement tanks are not really needed, unless you have a lot of dust in the air.

You have a huge catchment with that roof, why not think about collecting from every roof?

I sometimes use a fire pump to move large volumes of water, through at least 2 inch pipes, it uses less energy to do so.
The bigger the pipe the more efficient with the energy, bearing in mind the extra cost of the bigger pipe.
Anything less than 2 inch over 50 -100M is wasteful for fast transfer.

A local pump expert can help match pump capacity with speed of transfer to be most efficient.
You may be lucky and have a solar pump that can work independently of the house and pump all day when the sun is out.

By planning well ahead, one big tank down low and another up high above the house may work better.
The tank above the house should hold at least , say 3 months supply. And the lower tank be big enough to catch as much of the rain when it lands at the time it lands.
You may find 20.000L tanks around the buildings with an overflow to the lower tank may work, because each litre lifted a shorter height saves energy.

I am confident the energy pumping from the bore / well may be very high at the moment.

I use a firepump on wheels at 5 tanks and tramsfer the water to the master tank as needed.
I also have floating depth indicators on each tank, so I can glance across and see the level in each tank, it saves a lot of walking and is more efficient than electronic systems.

IT is a great idea

Using all the roofs is the better idea.
The tanks in that reply are really giant , what a water they can collect.

You may also interested to our project: http://gileboom.info/rainwater-harvesting/
Two 6000 Liter tanks plus one 500 liter till now and we will add one more.

Regards

Check out my cement pond video. I built in 2012. Its 32 ft wide 52 ft long stair stepped to  11ft deep 2 inches of cement covered chain link and chicken wire. It is for swimming fishing and irrigation. Its on the very highest part of my property and have no problem filling in the rainy season with the run off of my high tunnel.I dug a ditch and lined it with plastic and filled with gravel which leads to a 4 inch pipe and then into the pond. Crystal clear water, in my video you can see the bottom at 11 ft. Check it out on youtube
  if this link does not work my channel is william e   the video is called My cement pond

I would turn the roof upside down for rain shelter!