If you live in London, you have probably wondered whether bottled water is actually better than what comes from the tap. The honest answer is: in most respects, no. London tap water is safe to drink, more strictly regulated than most bottled water, and dramatically cheaper and less environmentally damaging. There are specific circumstances where filtration or even bottled water makes sense — but they are the exception, not the rule.

Regulation: tap water wins clearly

UK tap water is regulated by the Drinking Water Inspectorate (DWI), which tests thousands of parameters across millions of samples per year. Thames Water is legally required to meet over 50 water quality standards set out in the Water Supply (Water Quality) Regulations 2016. The compliance rate in 2024 was 99.97%.

Bottled water in the UK is regulated as a food product under the Natural Mineral Water, Spring Water and Bottled Drinking Water (England) Regulations 2007. Bottled water is tested far less frequently than tap water — typically by the bottler itself under manufacturer self-certification. Some parameters that tap water must comply with have no equivalent requirement for bottled water.

Quality: broadly comparable, with specific exceptions

In terms of microbiological safety, London tap water and reputable UK-bottled water are broadly comparable. Both are very unlikely to cause illness in healthy adults.

The specific areas where London tap water falls short of the "pure water" marketing image associated with premium bottled water are:

  • PFAS: Thames Water has active DWI PFAS improvement notices. Some premium bottled waters from remote springs have no detectable PFAS. See: Thames Water PFAS guide.
  • Hardness: London water is very hard (250–350 mg/l CaCO3). Many bottled waters are significantly lower in calcium and magnesium.
  • Chlorine: Tap water contains residual chlorine, which gives a faint taste many people dislike. Bottled water does not. A basic carbon filter jug removes chlorine taste entirely.

Cost: tap water is 500 times cheaper

London tap water costs approximately £0.001 per litre (0.1p per litre) at current Thames Water rates. Premium bottled water in a supermarket costs £0.50 to £2.00 per litre or more. A household spending £500 per year on bottled water could produce the same volume from the tap for approximately £1.

Environmental impact: bottled water is significantly worse

Producing a one-litre plastic bottle of water requires approximately 3 litres of water in total (including manufacturing) and generates around 250g of CO2 equivalent. UK tap water produces roughly 0.3g CO2 per litre. Even accounting for delivery logistics of mains water, tap water has a carbon footprint approximately 300 to 500 times lower per litre than bottled water.

When does it make sense to choose bottled or filtered water in London?

  • If you are pregnant or immunocompromised and concerned about PFAS: an NSF 58 RO filter is better than bottled water (more regulated, cheaper long-term, no plastic).
  • If you strongly dislike chlorine taste: a carbon jug filter solves this for about £30 per year.
  • When travelling or during specific incidents (boil notice, etc.): bottled water is sensible as a short-term measure.