Feature types and cost ranges
Self-contained water features — millstone bubblers, wall-mounted spouts, boulder features, column fountains — are the simplest category. They use a submersible pump in an underground reservoir, a decorative stone or fibre-glass feature, and require only a 13A socket connection (or a new Part P circuit if no socket exists nearby). Installed cost: £800–£4,000 depending on feature size and stone specification. Formal ponds — geometric or freeform, lined with EPDM rubber liner (Firestone PondGard, 1.02mm), with planted shelves, fish or purely ornamental — cost £3,000–£8,000 for a 10–20m² pond with filtration, UV clarifier and LED underwater lighting; £8,000–£15,000 for larger ponds with more complex filtration, cascades and hard coping detail. Rills — long, narrow channels of moving water typically set flush with a terrace or lawn — cost £5,000–£20,000 depending on length, pump capacity and stone or stainless steel finish. Natural swimming ponds — regeneration zone + bathing zone, designed without chemicals, relying on aquatic plants and biological filtration — cost £25,000–£80,000 for a complete project including excavation, liner, planting and plant room. These are the fastest-growing premium garden feature in outer London boroughs (Barnet, Bromley, Richmond, Merton) where plot sizes allow the required regeneration zone.
London hard water, pump maintenance and planning
London's mains water is classified as very hard (300–500mg/l as calcium carbonate), sourced from the Thames and Lee Valley chalk aquifers. Hard water deposits limescale on pump impellers (reducing flow by 30–50% within 12 months if untreated), on stone water features (white mineral crust), and on UV clarifier sleeves (blocking UV transmission and reducing effectiveness against green water algae). Annual descaling with citric acid solution (pump run in a bucket of citric acid solution for 2 hours) maintains pump performance. For pond water chemistry, hard London water is beneficial for fish health (high carbonate hardness buffers pH swing) but promotes algae growth — a correctly specified UV clarifier sized to the pond volume (turnover rate: total volume through UV unit every 2 hours) controls green water effectively. Planning: a pond under 4m² surface area does not require planning permission. A pond over 4m² in a conservation area or on a listed building curtilage may require planning permission if it constitutes an engineering operation. Natural swimming ponds always benefit from pre-application planning advice due to their scale.
