With ever-growing numbers wishing to get outdoors, and ever-warming temperatures in which to do it, carrying enough water to drink becomes a hot topic. These days the idyll of topping up from clear-flowing mountain streams untainted by agricultural run-off, livestock or human activity exists in fewer spaces in the UK. For those wanting to access clean water on the go there are a number of options, of which filtering is far more convenient than boiling and far more pleasant than treatment. At least it would be if filtering were simple and un-faffy and you could still carry decent amounts of water.

This is where Platypus' DayCap In-Bottle Filter comes in, launched in 2024 with the aim to make water filtration easy and accessible to a wider range of people. 

What kind of filter do you need?

Back in 2024, we reviewed Platypus' QuickDraw as "probably the best [solution] for hillwalking, running and climbing in the UK". 

So how does the DayCap add to the filtration offering? When considering what the DayCap is, it is also worthwhile considering what it is not. This is not a lightweight straw for sucking direct from the water source, and neither is it suitable for processing and decanting higher volumes of water in camp.

Primarily designed for use with a wide-mouth bottle, it is a quick, convenient and simple filter for a personal/family water bottle. For day hikes with access to water sources, it really is as easy as "scooping and drinking" - in fact so easy that our 3-year-old had no problem with it. It is also an excellent option for travelling in countries where you cannot trust the tap water yet want to minimise the plastic waste and cost of buying bottled water. We have also used it in the context of day ski-tours, for lightening the burden on communal water filtering in overnight hut trips, longer climbing days with convenient water sources and fastpacking on the Saunders Lakeland Mountain Marathon.

Compatibility

One of the strongest selling points of the DayCap is that it is sized to be compatible with popular brands of wide-mouth water bottles, so you can just add it to something you already have. Examples they give include Nalgene Wide Mouth, Hydro Flask Wide Mouth, Yeti Yonder and CamelBak Wide Mouth, which in most cases gives you the ability to filter up to 1L of water before refilling. For those looking to blur the lines into soft flask/water bladder territory, Platypus suggest the Nalgene Wide Mouth Ultralite, MSR Dromedary/DromLite, (which can also be used to perform integrity checks on the filter - see Maintenance). In testing, we've also found the cap thread is compatible with the Ortleib Water Bag, giving the option to use the filter and carry up to 10L of water, should you wish to! (N.B. Given soft bottles and bladders are not as suited to protecting the filter as a rigid bottle, we'd recommend taking the filter out during transport and adding when drinking.)

Weight and size

If compared to straw and soft bottle/bladder filters, the downside of the DayCap is that it (mostly) requires you to carry a rigid bottle which is heavier and bulkier than other solutions. However, in the context of its intended use, the beauty of the DayCap is that it will take up no more space in your pack than the bottle you were going to be carrying anyway. Though the whole system weighs 65g, assuming you're replacing an existing bottle lid with the DayCap cap, then the additional 20g weight of the filter cartridge is pretty negligible.

What it filters

The DayCap's removable filter utilises the same technology as Platypus' popular and award-winning filter systems including the QuickDraw. As you drink, the hollow fibre filter draws water quickly through a mass of tiny straw-like filaments with a pore size of 0.2 microns that removes 99.9999% of bacteria and 99.9% of protozoa including Giardia, Cryptosporidium, E. coli, Salmonella and Cholera as well as microplastics (the accumulation of which in the human brain has recently been linked with dementia and other neutrodegenerative diseases). It is also worth noting that though the filter will remove the bad stuff from your water, it will not necessarily remove bad tastes.

Though there are other products on the market that filter to 0.1 microns, the intended use of the DayCap means that 0.2 microns should be perfectly adequate for the vast majority of users.

The DayCap offers a flow rate of up to 1 litre per minute, depending on the how clear/silty your water source is and how hard you suck. As detailed below (Maintenance), Platypus recommend proactive cleaning via shaking on the go to maintain good flow. It also took us a few flushes through from first use to reach maximum flow rate, which isn't quite the "natural drinking experience" claimed in the product description but is definitely good enough.

The Cap

The cap component of the DayCap is made of a robust TPE material and is well designed, both for use with the filter, carrying around and as an everyday bottle lid. For example, it now permanently lives on my Nalgene as the flip-up cover is quick to open and the spout makes drinking easy, at any angle and on the move. (Yes, it prevents *that* thing where you're a passenger in a car trying to grab a quick drink from a wide-mouthed bottle and the driver suddenly accelerates leaving you with water all down your front...) It also has a neat valve which allows air to replace the water displaced by drinking so you don't get an annoying bubbling or drag as you drink. When flipped up the "spout seal" stays open and out of the way, and when flipped down, the rubber seal makes the bottle spill-proof. The DayCap's loop is also useful for holding on the move or securing to your pack.

Good value?

With an RRP of £40 and a cartridge life of 1000L, at 4p per litre this isn't the best value filtration option on the market. However, given the alternatives (getting ill, or for example vs the price of chlorine tablets or buying bottled water in the context of dubious tap water when travelling) it doesn't seem at all bad.

Maintenance

The cap component of the DayCap is dishwasher safe and the filter is easy to maintain. With water that isn't running clear, the hollow fibre pores can quickly become clogged, reducing flow rate when drinking. However, cleaning the filter in the field is very easy - just fill the bottle 1/2 full (unfiltered water will do) and shake vigorously for 30 seconds. Platypus recommend being proactive about cleaning and also give guidelines for best practice for disinfecting the filter and bottle with a diluted bleach solution when necessary.

When not in use, Platypus recommend that the filter component be safely stored in bag/container to prevent the accumulation of dust and debris. It is also worth noting that if wet hollow fibres are allowed to freeze they can break, so the filter should be kept close to the body or in your sleeping bag in freezing conditions to avoid loss of function. Similarly, though in most dropping situations the shell of the bottle and water will cushion the filter from impact, this is another situation where fibres could be broken and no longer safely filter water. For such cases, the DayCap instructions show you how to perform an integrity test using a squeezable wide-mouth bottle or bladder to check if the filter is still functioning safely.

If the filter is broken, or you feel you are reaching your 1000L cartridge life, replacement cartridges are available at £26.

Ethics and environment

As part of Cascade designs, Platypus make most of their products in the US, and support a range of conservation organisations.

Verdict?

An easy and robust solution for hydration on the move, the DayCap is a great option for those new to filtering, day hikers looking to reduce the amount of water they carry, and those travelling in areas where the tap water is suspect.