Drainage, septic tanks and soakpits
Almost nowhere around Nanyuki has mains sewer, so every house needs its own tank and somewhere for the water to go. It is concrete and masonry work, it is done while the foundations are being dug, and it is one of the few parts of a house that is genuinely unpleasant to put right later.
A septic tank and soakpit is commonly KES 180,000 to 600,000 depending on the size of the house and the ground.
Where it goes is decided early
The tank has to sit far enough from the house, far enough from any borehole or well, and low enough that the drains run to it by gravity. Those three constraints usually leave one sensible position on a plot, and It is worth finding it before the house is set out.
Falls matter more than people expect. A drain run laid too flat blocks; laid too steep, the water outruns the solids and it also blocks. None of this is clever. It is ordinary work done properly.
Why soakpits fail
A soakpit works by letting water disperse into the ground around it. On free draining murram that works well. On clay, and particularly on black cotton soil, the ground barely accepts water at all, and a soakpit sized as though it were on murram will surcharge in the first wet season.
Where the ground will not take it, the answer is a larger dispersal area, a soakaway trench, or a biodigester that discharges much cleaner water. Which one depends on the soil, and again the way to know is to dig and see.
Surface water is a separate problem
Roof water and surface run off must not go into the septic system. It overwhelms the tank and it is the reason a system that worked for two years suddenly does not. Gutters, downpipes and a drainage plan that takes surface water away from the house are part of the build.
On sloping plots the ground water arriving from uphill matters as much as the rain falling on the roof. A cut off drain above the house is cheap while the ground is open and expensive afterwards.
Questions people ask
How much does a septic tank cost in Kenya?
Commonly KES 180,000 to 600,000 including the soakpit, depending on the size of the house and what the ground will take. Black cotton soil pushes it up, because the dispersal has to be larger or replaced with a biodigester.
How far should a septic tank be from the house?
Far enough that there is no smell and no risk to the structure, far enough from any borehole or well to protect the water, and positioned so the drains run to it by gravity. Those constraints usually settle the position between them, and it should be worked out before the house is set out.
Why does my soakpit fill up and overflow?
Usually one of two things. Either the ground will not accept water at the rate the pit was sized for, which is common on clay and black cotton soil, or surface and roof water is getting into the system and overwhelming it. The second is much more common and much cheaper to fix.
Is a biodigester better than a septic tank?
It is better where the ground will not take the discharge from a conventional soakpit, because the water leaving it is far cleaner and needs a much smaller dispersal area. On free draining ground a well built septic tank and soakpit does the job for less money.
Planning drainage?
Tell us the plot and roughly what you have in mind. We will come and look, then give you an itemised figure.