A small utility team looks at a reservoir that serves the whole community and asks the obvious question. Can we clean it without emptying it? Often, yes, but with strings attached. The facility, the sanitary plan, the access and the owners requirements all have to line up first.

Thats the real story behind in service work. Ven Tech Subsea runs ROVs, robotic vacuums and potable grade divers for exactly this, and the sanitary side follows AWWA cleaning and inspection principles. Lets go through what has to be true before a tank stays full.

The short answer, with strings

Water reservoir cleaning and inspection while the tank remains full or isolated full is a real option in the Ven Tech Subsea approach. Where the asset, water quality objectives and owner requirements permit, the work can be done without draining. That can reduce treated water loss and shorten the time a storage asset sits unavailable.

But its not a promise. Ven Tech says every recommendation is based on the facility, not on a one method sales line. If the structure, the water or the sanitary controls dont support in service work, the honest recommendation changes. Better to hear that early than halfway through a mobilization.

What in service really takes

The 2025 edition of AWWA C652 recognizes that a tank can stay in service, or be isolated, for minimally intrusive ROV or diver inspection when the sanitary and operational plan supports it. Notice the wording: minimally intrusive. This isnt a licence for any kind of work at all.

So the plan looks at construction, volume, access, water use, isolation, circulation, previous reports and known water quality concerns. The owner keeps control of system operation and return to service. Ven Tech helps compare the operational tradeoffs, and then everyone picks the approach with eyes open.

Robots that vacuum

Compact ROVs, utility crawlers and robotic vacuum systems can inspect and clean suitable reservoirs while keeping personnel outside the water storage environment. HD video gives live client viewing, sonar helps in low visibility, and magnetic crawlers plus project specific NDT can support suitable steel tanks.

The vehicle, tether, camera, lighting, sonar, cleaning head and retrieval plan get chosen around access and the required result. Small hatch? That narrows options. Big floor with fixed internals? That changes the cleaning route. Its all geometry, really, and a bit of patience.

Divers where hands matter

Some jobs need touch. Surface supplied commercial divers provide close observation, controlled sediment vacuuming, localized cleaning, hands on checks and minor intervention, with live comms and topside video. Diving configuration, team size and entry controls match the jurisdiction and risk profile.

Ven Techs equipment is potable only or properly segregated, with a documented disinfection procedure. A 200 ppm chlorine solution is commonly used for ROV, tether and diving equipment when appropriate to the approved plan. Divers and robots both follow that same sanitary discipline, because the water doesnt care which kind of crew entered.

Standards in the background

AWWA cleaning and inspection work leans on C652, a disinfection standard. The 2025 edition adds a disinfection plan, and a dechlorination plan when warranted, along with chemical handling precautions and clearer chlorine terminology. Ven Techs field plan names the products, concentrations, handling and records for each agreed job.

What the standard doesnt do is describe how to inspect. That technical route is separate, and its built from the owners questions. So in practice youve got two layers: sanitary control from C652, and an inspection method designed around the reservoir. Mixing them up is where projects get muddled.

Real jobs: Cowichan Bay and Penelakut

Ven Tech Subsea shares a few examples. At a potable reservoir in Cowichan Bay, 100 feet across, work was completed under sanitary commercial diving controls, with zero reported WorkSafeBC violations, deficiencies or orders in the documented site inspection.

For the Penelakut Tribe, the company supported inspection and cleaning of a 50 foot reservoir, again with zero reported violations, deficiencies or orders in the recorded site inspection. Different sizes, same planning habits. Those small details, like documented alignment with diving and potable water procedures, are what a utility procurement team actually reads.

Hold points and handback

Water quality checks come with agreed hold points. Chlorine residual and turbidity observations are recorded, and coliform sampling and lab analysis get coordinated with the owner or a qualified laboratory. The owner decides acceptance.

At the end, the sanitary record gets closed out: equipment preparation, concentrations, times, observations, deviations and media. It all goes into one package. When the tank returns to service, nobody should have to wonder what happened inside it.

FAQs

Can a potable water reservoir stay full during cleaning?

Potentially, if the facility, water quality objectives, sanitary controls, access and proposed work support it.

Does an ROV replace divers?

Not always. ROVs suit remote inspection and cleaning. Divers suit touch, dexterity and direct intervention. A combined plan is common.

What does the 2025 AWWA C652 edition add?

A required disinfection plan, a dechlorination plan when warranted, chemical handling precautions, clearer chlorine terms and updated guidance on positive coliform results.

What does water reservoir cleaning and inspection cost in downtime?

That depends on the facility. Working in service or isolated full can reduce treated water loss and downtime compared with draining, when conditions allow.

The short version

Water reservoir cleaning and inspection can often happen without draining, as long as the sanitary plan, access and owner requirements support it. AWWA cleaning and inspection principles frame the disinfection side, while divers, ROVs and robotic vacuums handle the actual work. If youre weighing a drain down against an in service job, share your tank details with Ven Tech Subsea.