How much water do you need, and how do you carry it all?
In the Simpson Desert 101 series, I talk through planning our first Simpson Desert crossing. Hopefully this will be useful for those planning their own expedition. I will update these posts post-trip with our real-world experience.
In this post:
How much water do you need?
One of the biggest worries for first-time desert travellers is water. How much will you need? How do you carry it all? What if you run out?
Our family of four allows about twenty litres of water per day between us on desert expeditions. I know this from accumulated experience, but here's how I work that out. Hopefully you can use these numbers to estimate your own use.
Drinking
In the Defence Force, we used to be taught the basic ration for indefinite survival is two litres, per person, per day. Add one litre per hour of exercise or sun exposure. You can survive on half these figures, but not for long. Under this formula we need eight litres per day between the four of us.
The National Health and Medical Research Council is a bit more scientific and recommends varying fluid intake figures based on age and sex. These range from 1.0 litres per day for a baby (in the form of milk) through to 2.6 litres per day for an adult male or a breastfeeding female. These values assume you're otherwise fit and healthy, you're eating a normal diet, and you won't be vigorously exercising.
Using the NHMRC figures, my kids need 2.4 litres per day between them, and the adults need 2.1 and 2.6 litres, for a total of 7.1 litres. Because it's possible I'll be cracking a sweat from time to time digging myself up and over a dune, I'm going to allow a little extra and round that up to 8 litres per day.
Note that we also carry soft drinks, light beer, and fruit juice, which I am not counting in my eight litre ration. These sources of fluid are perfectly fine to keep you hydrated, despite old wives' tales to the contrary (see the NHMRC link above if you don't believe me), but are not effective at re-hydrating you if you become dehydrated. Best to stick to water if you're out in the sun or doing hard manual work, and keep the fun stuff for dinner time.
Total: 8 litres
Cooking
It's hard to quantify how much water you'll need for cooking. It depends what you cook and how you cook it. In the desert, we try and avoid meals that require cooking with water. But if you're a real gourmet, or you plan on using dehydrated foods, you'll need to add up all of the water your recipes require and add that to your total, plus a bit for Mum to account for spills (perhaps 5% or 10%).
On average, I'd say we use less than one litre per day for cooking. On many days, it's none. But when we do use water for cooking, it's to heat a can by standing it in water, or to cook dry pasta, and we usually re-use that water for washing up so it's a net zero use for us.
Total: 0 litres
Washing up
How much water you need for washing up depends on how often you wash up, and how large your sink or bucket is. We use the built-in sink on our camper trailer, and it takes the contents of our 1.5 litre kettle (boiled) plus the same kettle re-filled and poured in again cold to get the right depth and temperature. That's three litres per wash.
We try and limit the amount of washing up to be done - cooking is generally done all in one pan, for example - but we find with four of us we wash up twice a day most days.
Total: 6 litres
Hygiene
Hygiene covers hand washing, bathing/showering/whatever to keep yourself clean, and cleaning teeth.
We do most hand washing with sanitiser - outback tourers were buying that stuff in bulk well before COVID19 - and if hands are heavily soiled, we use waterless hand wash like this. Unlike sanitiser, you have to wipe this off with a towel but it's far more effective at removing actual dirt.
We clean our teeth by filling a mug with about an inch of water. Dip the brush, put paste on it, brush, rinse your mouth, clean the brush head in what's left in the mug. This water can come from your surplus cooking water or your daily drinking ration - as long as you don't rinse under running water, you won't use much. We don't really count this usage.
For washing the rest of the body, we use an old fashioned hot sponge bath. You fill a small bucket with warm water, use a face washer to wet the body bit-by-bit, apply soap to the wet bits, then wipe the soap off. We can do this with as little as two litres of water if we all share the same water, but we usually swap it out between boys and girls for a total of four litres. Draw straws about who gets to go first! It sounds gross but this is basically how your all of your forebears before the 1950s washed themselves every day.
You can supplement whole body washing with baby wipes of the hands and face, if you're not particularly dirty or stinking.
We haven't previously used camp showers for desert travel (although they're very nice for trips closer to civilisation), because they simply use too much water. Most hot shower units flow at about two litres per minute at their lowest (barely adequate) setting, so a two minute shower uses four litres per person, PLUS you usually lose a further two litres 'trapped' in the hose and pump. So even if we showered every second day (boys on one day and girls on the next), we'd use ten litres per day. This is simply unsustainable in an environment with no access to fresh water.
If you do want to use a shower, the technique is to wet yourself down, turn off the shower, soap up, and then turn the shower back on to rinse. That's how you get it done in two minutes.
We have recently picked up an Evershower unit which is very efficient at continuously recycling your own shower water, permitting higher flow rates and much longer and more satisfying showers. The manufacturer claims about five litres is perfect, although it can work with less. If true, we could shower two of us every night (sharing the same water) for five litres per day. So on our next trip we're going to try this out. I'll write a post on how that works out.
Total: 4 litres (temporary increase to 5 litres for Evershower trial)
Laundry
For the Simpson, you're not going to need to do laundry. Just pack enough clean undies to make it through, it's only a week at the longest! Rule a line under the last paragraph and call it done at 18 litres per day.
For longer expeditions you will need to do laundry even in very remote country - there's only so many pairs of undies you can carry! We use a Scrubba wash bag, and ours takes about five litres to wash and five litres again to rinse. We wash underpants and socks only - everything else can remain filthy until we hit town. We do this every five(ish) days, so let's call that an average of two litres per day if you want to convert that to a daily figure.
Total: 2 litres
Emergency supply
We can carry up to 160 litres of water, enough for up to eight days, and longer if we can supplement our water from creeks, dams, bores etc. However, it's unwise to carry only as much water as you think you'll need. What if you're delayed a day, or someone gets sick and needs extra water? We usually budget for at least an extra couple of days.
We also carry a 15 litre cask or a 24-pack of 600ml bottles which we don't plan to use. That's two days of drinking water for the four of us in a dire emergency or an easily-handled emergency supply we can give to someone else. It can also be used for first aid - to clean a wound, flush a dirty eye, or wet down a burn dressing.
Total
Our minimum use is 18 litres per day. Allowing for the shower, it will be 19 litres per day. If we planned on doing laundry too (we don't on this trip, but we do on others) then it's 21 litres per day.
We plan to cross the Simpson in five days, but we will carry water for seven. So our total water requirement is 7x19=126 litres.
How to carry it
However you can, really. But there are two important rules:
Don't carry it all in one container or tank
Don't carry it on the roof.
If you carry all your water in one tank, you're one unlucky hit from a rock or one popped drain bung away from losing everything. Once we came across a family with a toddler on board halfway up Googs Track in a Patrol. They had an under-body water tank and had knocked the spigot off on an unfortunately-placed mallee root the day before. They had now been 24 hours in the desert with no water. They were heading to Glendambo to get more, at least a full day of driving away. We were able to hand over our 15 litre emergency cask to get them through the day.
We carry the bulk of our water (85 litres) in our trailer's built-in tank. We have a further 35 litres built into the 200's rear drawer system (bringing us up to 120 litres), and can carry up to two additional 20 litre jerry cans in holders (bringing us up to 160 litres), although we prefer not to carry the jerries.
For the Simpson we plan on 126 litres, so we will carry the two full tanks plus one jerry can for a total of 140 litres, plus our 15 litre emergency supply.
One thing you should not do is carry water on your roof rack - water is really heavy and putting it up there will significantly increase the risk of your vehicle rolling over. It's also more vulnerable to damage from trees that hang over the track, and it spends all day in the sun. No one wants a refreshing drink of scalding water after digging you out of a bog.
If you don't have the luxury of built-in tanks like us, you can look at options such as flat panel water tanks that fit behind your rear seat; floor well water tanks that the kids can stand on; or just lots of small bottles and containers scattered wherever they'll fit.
Flat panel and footwell style water tanks - each of these is 40L
What about purification?
In the hiking and boating worlds where it isn't possible to carry all the water you'll need, they carry water purifiers. These generally fall into two main types - filters and treatments.
Filters, such as a reverse osmosis pump, strain all the bugs and nasties out of the water and can produce large quantities of water, but they're bulky and slow. They're very popular in boats where they can run continuously. You can also get straw-like water bottle inserts, but these really suit individual survival use only.
Treatments include chemical tablets and UV sterilisation. These are lightweight and portable and can produce drinkable volumes quickly. These are the preferred options for hikers.
Neither option is really suitable for you to rely on in the desert as your primary source of water - they both rely on finding water just lying around. With a few exceptions, for the most part you can't do that in the outback - at least, not any more conveniently than you can carry water yourself.
The Canning Stock Route is a notable exception, as it was originally built to connect a series of natural and artificial wells, some of which remain in good order. It's best not to rely on them, especially for drinking, but they are there. Just beware you may arrive to find the well dry, or filled with rotting cow carcasses, or vandalised.
Small, emergency treatments or individual filter bottles might be a good idea for your emergency kit or grab bag, but you will still need to plan your trip (and potentially your vehicle build) around carrying enough water.
Water hacks
A couple of quick notes - regardless of how you carry your water, ensure that you always separate water from a known potable supply (such as town water) from water of unknown quality (such as water pumped from a stream or bore). That may mean you need two tanks or spare jerry cans if you intend to gather water this way. If that water you collect turns out to be bad, this way it hasn't contaminated all of your water, just the tanks or containers it was in. Water-borne disease kills more people globally each year than any other disease vector.
It's always handy to keep at least one container of a size you can easily handle - five or ten litres perhaps, depending on your build - that you can use to carry to wash in private or fill up from a source you can't drive to.
A simple siphon and funnel will help you transfer water from big tanks or containers to smaller ones that you can handle and pour more easily.
Simpson Desert planning
There is always water in the Simpson at Dalhousie Springs and Purni Bore, however neither is suitable for drinking or cooking. There is no water available between Purni Bore and Birdsville. Even after a wet season, the clay pans and creek lines that flow are either silty, salty, or both. You should plan to carry all of your water for the full crossing.