What Size Berkey For A Family Of Five?
The Royal is the right size for five people. Here is the arithmetic behind that, why five crosses a threshold that four does not, and why the element count matters more than the tank.
For five people, the Royal is the right size, fitted with four elements rather than two.
Five is the point where a Big Berkey stops being adequate, and the reason is not simply that five people drink more than four. It is that the fifth person changes the shape of the demand, not just the size of it.
Why five crosses a line
Water use in a household is not spread evenly through the day. It comes in a burst in the morning and a smaller one in the evening, and the morning burst is what decides whether a filter feels adequate.
Adding a fifth person adds perhaps 20 per cent to the daily total. It adds considerably more than 20 per cent to the morning, because that fifth person wants their bottle filled in the same ninety minutes as everyone else.
Five people between seven and half past eight want: five water bottles, two kettles, and glasses at breakfast. That is seven or eight litres inside an hour and a half.
A two-element system produces roughly five litres in that time. So it does not just fall slightly short — it falls short at exactly the moment when nobody has time to wait for it.
This is why the answer for five is not "the next size up" but "the next size up, with more elements". The tank stops it running out. The elements stop it running slow. Five people need both.
The arithmetic
Work out your own figure rather than trusting a rule of thumb, because households vary enormously.
Drinking: 1.5 to 2 litres per adult, less for younger children. For five, call it 7 to 9 litres.
Tea and coffee: a litre and a half a day is conservative for five people, and a household of tea drinkers will do more.
Cooking: two litres a day for a family of five eating properly — pasta, rice, vegetables, stock.
Bottles out of the house: five at half a litre is two and a half litres, and all of it leaves in one go.
Pets, squash, ice: another litre or so.
A family of five filtering everything lands between 14 and 20 litres a day. Filtering only drinking water and hot drinks brings it down to around 9 to 12.
Then check it against production. A pair of elements produces roughly 3 to 4 litres an hour. Sixteen litres a day at 3.5 an hour is four and a half hours of filtering, which is fine spread out and impossible concentrated.
Tank size and flow rate are different problems
The distinction that decides most of these purchases.
Tank size is how much the upper chamber holds. It decides how often somebody refills it.
Flow rate is how fast filtered water appears, and it is set entirely by the number of elements. Gravity is the only force involved, and each element passes what it passes.
A Royal fitted with two elements filters no faster than a Big Berkey fitted with two. It simply holds more between refills.
So buying the bigger model without adding elements solves half the problem. For five people it is the wrong half, because the complaint that actually bites is speed rather than capacity.
Four elements roughly double the flow. They do not shorten each element's life — the total volume the set can handle is unchanged, so four elements last about twice as long as two doing the same work. The upgrade costs less than moving up a model size and does more.
What the Royal gives you
Around twelve litres of tank, taking up to four elements.
With four elements it produces roughly 7 to 8 litres an hour and holds twelve. That covers a five-person morning peak from a full lower chamber, and it recovers within the working day.
With two elements it holds enough and produces about half what five people want at peak. It works if somebody fills it every evening without fail. It does not work otherwise.
The evening filling habit is the single most useful thing in any of this. Fill the upper chamber before bed and the filter has all night at its own pace. The morning then draws on a full lower chamber rather than waiting for production.
Two systems instead of one
An option worth considering for five people, and one that rarely gets mentioned.
Rather than one large unit, some households do better with two mid-sized ones in different places — one in the kitchen and one upstairs, or one in the kitchen and one in a utility room.
What it gives you: twice the total element count, so twice the flow. Two points of use, so nobody queues in the morning. And redundancy, because if one develops a problem the other carries on.
What it costs: two lots of worktop space and two systems to clean and maintain.
It is not the obvious answer and it suits some households better than one big unit, particularly where the house is spread out or where the morning rush is genuinely the problem.
Reserve capacity
An argument that applies more to five people than to fewer, because larger households are harder to supply in an emergency.
A gravity filter needs no power, no pressure and no plumbing. When the mains fails — a burst main, a contamination incident, a boil water notice — it will make stored water, rainwater or water from a questionable source drinkable, and it will do it during a power cut.
Five people drinking two litres a day is ten litres a day of bare minimum. A filter with a twelve litre tank and a full lower chamber is roughly a day's supply already standing in the kitchen, and it will keep producing as long as you can feed it water.
This is one of the better reasons to buy a gravity system at all rather than a plumbed one, and it argues mildly for the larger tank even if your daily use would not require it.
Do not buy larger than you empty
The counter-argument, and it is a real one.
Growth in these systems is caused by water standing still with no chlorine left in it. The filter removes the chlorine, which is the point, so filtered water in the lower chamber has no residual protection at all.
A household that empties its lower chamber daily gives bacteria and mould almost no opportunity. A household with a system twice the size it needs is permanently holding several days of water, which is exactly the condition that causes problems.
For five people this is rarely a concern, because five people turn over even a large system. It becomes a concern if you buy for a household of five and then it becomes a household of two. The guide to growth in gravity filters covers what to look for and how to prevent it.
If the five includes small children
Adjust downwards, and be careful how far.
Young children drink considerably less than adults, so five people including two under-eights is closer to a demand of four adults than five. The Big Berkey with four elements may well be enough.
Two things argue against sizing down too far. Children grow, and a teenager drinks more than an adult while being entirely unreliable about refilling anything. And households with small children tend to do more cooking and more squash-making than households without.
If money is tight, a Big Berkey with four elements now and a bigger tank later is a reasonable path, because the elements move across.
Practical checks before buying
Height and filling clearance. A Royal is tall, and you need room to lift the lid and pour a jug in above it. Measure from the worktop to the underside of the wall cupboard.
Weight when full. Twelve litres is twelve kilograms plus the unit and the water in the lower chamber. Check the surface takes it and make sure nobody tries to move it full.
Tap height. A tall glass under a low tap is a daily annoyance. Buy the stand at the same time.
Distance from the sink. If it lives across the kitchen, somebody carries jugs several times a day. Next to the tap is better.
Out of direct sunlight. Light causes algae in the chambers.
Element cost over five years. Work out the annual figure before committing. Elements last a long time but they are the whole running cost, and adding fluoride reduction elements changes the picture significantly because they are on a much shorter cycle.
Making a system faster without buying anything
Before spending money on a larger unit, four things affect the flow rate and three of them are free.
Keep the upper chamber full. Gravity systems slow down as the water level drops, because the pressure driving water through the elements is the weight of the water above them. A chamber that is a quarter full filters noticeably slower than a full one. Topping it up as it goes down, rather than waiting for it to empty, keeps the flow at its best.
Clean the elements. This is the big one, and it is the answer most of the time when a system that used to be fine has become slow. Sediment builds a cake on the outer surface and chokes the flow. Scrub them under cold running water with a stiff pad — no soap — and re-prime them. On mains water this is a job for every few months; on cloudy water, far more often.
Re-prime after cleaning. Air trapped in an element blocks it as effectively as sediment does, and an unprimed element is regularly mistaken for a faulty one. If flow is poor after cleaning, prime again before concluding anything.
Pre-filter dirty water. If you are filtering anything cloudy, straining it through a cloth first keeps the elements clean for far longer.
Do all four and a system that felt inadequate often turns out to have been merely neglected. That is worth checking before deciding you need a bigger one.
Where a gravity filter stops being the right answer
Worth saying, because for some households of five it is not.
A gravity filter is a point-of-use system. It treats the water you pour into it and nothing else. Everything else in the house — showers, baths, the washing machine, the outside tap — is untouched.
If your reason for filtering is chlorine and skin, five people means five sets of showers a day, and no countertop system addresses any of them. That is a job for a whole house filter or for shower filters, and the guide to whole house water filters covers what that involves.
If your reason is fluoride, nitrates or dissolved solids, a gravity system needs separate specialist elements for fluoride and does nothing about the others. Reverse osmosis under the sink is the thorough answer.
And if refilling a chamber twice a day for five people is going to become a chore that nobody does, a plumbed under-sink filter takes the human step out entirely. It needs power in some configurations and it always needs plumbing, and in exchange it never needs filling.
The gravity system stays the better choice when you want no plumbing, no power dependency, portability, and something that works when the mains does not. For a lot of households of five those are exactly the priorities, which is why it remains the usual recommendation.
A decision rule for five
Five people, filtering everything, busy mornings: Royal with four elements. The default answer.
Five people, drinking water and hot drinks only, reliable evening refilling: Royal with two elements, or Big Berkey with four.
Five including two young children: Big Berkey with four elements is likely enough, with room to move the elements to a bigger tank later.
Five on a private supply, or wanting real emergency reserve: the next size up again, with the maximum element count.
Five where the morning rush is the actual problem: consider two mid-sized systems in different rooms rather than one large one.
The short version
The Royal, with four elements. Five people is roughly 14 to 20 litres a day filtering everything, and a twelve litre tank with four elements covers both the volume and the morning peak.
The mistake to avoid is buying the bigger tank and leaving the minimum elements in it. Tank size stops it running out; element count stops it running slow. Five people need both, and elements are the cheaper half of the fix.
Fill it every evening and the morning takes care of itself. If your household is four rather than five, the sizing for a family of four covers where the smaller system is genuinely enough.
