WATER

Drinking water apart, the absolute realistic minimum water consumption is about five litres each person per day. This is not a comfortable amount. It requires washing with a wet flannel and half a mug of water, and even less for cleaning teeth.

In cool weather, we each need to drink at least two litres of water a day, two to four litres in warm weather, and six or even more in very hot weather. One may need even more if exposed to wind and/or sun.It is important to maintain these levels. If you don’t you may end up with any number of medical conditions — particularly muscular cramps. It is even more necessary for babies and very young children. Dehydration symptoms include thirst, or loss of skin elasticity (pinch test on back of hand).

Fifteen litres a day allows a preliminary soaping up, plus two or three litres for a quick shower. A more realistic amount is twenty litres/person/day. If you travel in truly remote areas (particularly in my home area of the Kimberley where water is scarce outside towns), add an extra 20 litres/person/day.

Tanks

Bearing in mind that water weighs one kilogram per litre (plus about 20% more for the tank etc) it requires only a second or two’s reflection to realize this represents a lot of weight. A large motorhome may well carry 300 litres of fresh water — about 360 kg including all the associated bits. This is why it is so essential to keep other weight to the minimum — because this is an area where you really cannot compromise.

When building one’s own vehicle many people try to fit the ready-made commercial tanks sold by caravan accessory houses. But unless you can find tanks that are exactly what you need it pays to have stainless steel tanks made to the exact size you need. The work can be done by any good sheet metal fabricator for much the same price as off-the-shelf units. You need to shop around though: quotes may vary from $200-$750 for the very same tank.

Some fabricators will attempt to talk you into using aluminium, but I’m wary of these for health reasons, and also the likelihood of long-term corrosion. When designing your own tanks remember that you must have a separate outlet that vents to atmosphere, at least 100 mm above the top tank level. If you don’t only a tiny amount of water can be pumped in and out.

There’s a really good case for having two totally independent water systems, duplicated completely even (ideally) for taps. This ensures you have at least some usable water in the event of a tank being holed, or the water adulterated.

Water Pumps

Water is curious stuff. It is totally incompressible and has a strong objection to being pumped. In some ways the stuff is like electricity and analogies are often made between voltage (pressure), current (amount of flow) and watts (total pumped).

In practice though water does not flow as readily as electricity: its resistance to being moved through a small diameter pipe is phenomenal. It is proportional to the fourth power of pipe internal diameter! So, like motorhome wiring, but even more so, it pays to use piping that is a bit larger than you might have had in mind.

I strongly recommend then that you specify 16 mm rather than the 12 mm normally used. This will be reflected in less current being drawn by the pump, and tech notes WATER "we lived for days on nothing but food and water" - WC Fields only marginally complicated by the need to shop around for the larger diameter pipes and fittings (Whitworth’s Nautical World carry a wide range of sizes).

Most caravan-type twelve-volt electric pumps deliver 8-12 litres per minute at pressures of about 200 kilopascals (30 psi), but few do anything like that once installed, unless you use at least 16 mm pipe and fittings. It’s also a good idea to avoid right angle bends — better by far to have a bit longer pipe running in a curve.

These pumps typically draw 4-7 amps whilst running, but at least twice that whilst starting. Specify cable to cope with the starting current or you will run into pump problems if the battery runs low.The simplest pumping systems have a switch (often inbuilt into the tap) that starts and stops the pump. This is simple and effective, but involves running cables from each switch to the pump.

Most systems nowadays use a switch that is actuated by pressure in the water pipe (these switches are also commonly inbuilt into the pump). They initially switch on the pump until a preset pressure is maintained in the pipe (typically at 30 psi) from the pump to a tap. Then the switch cuts out and the pump stops.When a tap is turned on, the switch detects the drop in pressure. When pressure drops to (say) 20 psi, the switch closes and the pump starts up again.

There are two downsides to this. One is that it is essential to have really good connections as, in the event of a leak, the pump will keep going until the tank runs out — flooding the motorhome. Secondly, the pump may (and often does) start up for a second or three in the middle of the night to correct minor pipe expansion changes etc.This can readily be fixed by adding a pressure tank.

This is explained in my book ‘Motorhome Electrics’ but is beyond the scope of this article.The simplest way to connect up the various bits is via ‘snap together’ systems, but as far as I am aware these are not made to fit pipes larger than 12 mm.This is no big deal as it’s not that much more effort and is a lot cheaper to use (stainless steel) wormdrive hose clips.

(Hint, when tightening use a small socket spanner not a screwdriver as it’s only too easy to have that screwdriver slip and badly injure one’s hand.)

Hoses and Fittings

As only short runs are required, it’s well worth using food-quality hose. It costs a bit more and is harder to find — but once again you’ll find it at boat chandlers such as Whitworth’s Nautical World. Use hot water hose for hot water systems — normal hose tends to soften, causing connections to leak. Avoid cheap chain-store hose.

If including a mains water connection it’s best to include a pressure reducer as non-domestic bits and pieces will not withstand the generally much higher mains water pressure.

Filtering

This is certainly necessary but there is no need to go totally overboard. The main risks are giardia (faecal contamination) and cryptosporidium, but there are other bugs around that can cause tummy upsets.

A good setup is a simple mesh filter before the pump, followed by a 10 micron paper filter and a 1.0 micron paper filter after the pump. Paper filters work just fine but need replacing every year or so or they start to introduce more bugs than they trap. Silver iodide and activated carbon filters work better still but tap delivery will be very slow at normal dc pump pressures.

Reverse osmosis works even better but you typically only retain 10% of the treated water — the remainder gets dumped as part of the process. It’s both impracticable and overkill in our type of usage.Insist on having ‘standard’ industry-sized filter housings — as you then have a wide choice of cheaper filters.

I’ll discuss water heating in a later Tech Notes, but if you need to know about it right now it’s covered in ‘The Campervan & Motorhome Book’, available for $37 incl postage through the CMCA’s NHQ.